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Two wireless outfits built by boys. 



(Courtesy of the "Electrical Experimenter.") 



Frontispiece. 



American Boys' Book 



of 



Electricity 



By 

CHARLES H. SEAVER 



# 



PHILADELPHIA 

DAVID McKAY, Publisher 

608 S. Washington Square 






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Copyright, 1916, by David McKay 



OCT il 1916 



f U'* 



CI.A438813 



CONTENTS 



CHAPTER I PAGE 

Magnetism and Magnets u 

Discovery of the Magnet. — How the Magnet was Named. — 
Stories of the Compass. — Old Forms of Compass. — Modern Com- 
pass. — Agonic Line. — Magnetic Dip. — Experiments with the 
Magnet. — Making a Magnet. — A Simple Compass. — North 
and South Poles. — Robert Norman's Experiment. — Attraction 
and Repulsion. — Magnetic Field of Force. — Magnetism by In- 
duction.— The Earth a Magnet.— Magnetic Materials.— Theory 
of Magnetism. — Paramagnetic and Diamagnetic Substances. — 
Making a Permanent Magnet. — Care of a Magnet. 

CHAPTER II 

Static Electricity 27 

Static Electricity Everywhere. — Generating Static Electricity. — 
Where the Word "Electricity" came from. — How Static Elec- 
tricity has helped Science. — Difference Between Static and 
"Current" Electricity. — Gilbert's Discoveries. — Paper Electro- 
scope. — Positive and Negative Electricity. — Gray's Experiments. 
— Conductors. — Non-conductors. — Speed of Electricity. — Frank- 
lin and His Kite. — Apparatus for Easy Experiments. — "Pie- tin" 
Electrophorus. — How the Electrophorus Works. — Leyden Jar. — 
Van Muschenbroeck's Surprise. — Electroscope. — Making a Gold 
Leaf Electroscope. — An Easily Built Discharger. — Cylinder Elec- 
tric Machine. — Static Experiments. — Charging and Discharging 
Jars. — Series and Parallel Connections. — Precautions. — Lightning. 
— Thunder House. — Artificial Shipwreck. 

CHAPTER III 

Electric Batteries and Galvanic Electricity 61 

What the Battery Does. — Electric Current. — A Doctor's Dis- 
covery. — Volta's Battery. — Difference Between "Cell" and 
"Battery." — Zinc-copper Cell. — Flow of Current in Cell. — Elec- 
tromotive Force. — Action of Cell. — Polarization. — Local Action. — 



4 CONTENTS 

PAGE 

Forms of Cell. 1 — Carbon-cylinder Cell. — Leclanche Cell.— Gravity 
Cell.— Dry Cell.— A Glance Inside the Dry Cell.— Making Cells — 
Leclanche Cell Made From a Milk Crock. — "Tomato-can" Cell. — 
Making a Dry Cell. — Single-fluid Cells. — Electropoian Fluid. — 
Arranging and Mounting Electrodes. — How to Mix Depolarizing 
Solution. — Handling Chemicals. — Battery Connections. — Storage 
Cells. — How to Make a Storage Cell. — Choosing the Right Cell. 

CHAPTER IV 

Electric Circuits 86 

Circuit in a Battery. — Closed Circuit. — Open Circuit. — Voltage 
and Current. — Volt. — Ampere. — Resistance. — Insulation. — Short 
Circuit. — Ohm. — Ohm's Law. — Watt. — Kilowatt. — Series and 
Parallel Connections. 

CHAPTER V 

Electromagnets 95 

Magnetism from Electric Current. — Oersted's Experiments. — 
Magnetic Field Around Wire. — Solenoid. — Electromagnet. — 
Solenoid from Wire and Paper Tube. — Uses of Solenoids. — Uses of 
Electromagnets. — Electric Bells. — Making an Electric Bell. — 
Wiring a Bell. — Reliable Burglar Alarm. — Three-call Annuncia- 
tor. — Induction. — Induction Coils. — Primary and Secondary 
Windings. — Making an Induction Coil. — Spark Gap. — Experi- 
ments with Spark Coil. — Geissler Tubes. — X-Rays. 

CHAPTER VI 

Electric Heat 139 

Electric Current Changed to Heat. — Heating Effect of Different 
Metals. — Using Electric Heat. — Stored Up Energy. — Sunlight 
the Source of All Heat. — Economy of Electric Heating Appliances. 
— Heating Elements. — Electric Flat-iron. — Repairing the Flat- 
iron. — Making an Electric Toaster. — Other Uses of Electric Heat. 
— Electric Furnace. — Electric Arc. 

CHAPTER VII 

Electric Light 149 

Heat and Light Alike. — Vibration of Molecules. — Colors. — Prisms. 
— Direct Light. — Reflected Light. — Brightness.— What a Candle- 
power is. — Sizes of Electric Lamps. — Arc Lamp. — How the Arc 
Lamp Works. — Discovery of the Arc Lamp. — Sir Humphrey 
Davy's Lamp. — Jablochkoff's Lamp. — Principle of Arc Lamp. — 



CONTENTS 5 

PAGE 

Arc Lamp an Outdoor Lamp. — Mercury-vapor Lamp. — Incan- 
descent Lamp. — "Dividing" the Electric Light. — Platinum Fila- 
ments First Used. — Edison's Discovery. — Many Filaments Tried. 
— First Lighting Plant. — First Central Station. — Improvements. — 
Mazda Lamps. — Tungsten. — Use of Platinum in Lamps. — Minia- 
ture Lamps. — Voltages. — Lamp Bases. — A Handy Electric Lan- 
tern. — Electric Clock Light. — Dark-room Lantern. — Sizes of 
Miniature Lamps. 

CHAPTER VIII 

Electric Generators 168 

Sources of Electric Power. — Generation of Power. — Faraday's 
Generator. — Principle of the Generator. — Direction of Current. — 
Fleming's Right Hand Rule. — Commutator. — Field Magnets. — 
Residual Magnetism. — Series, Shunt, and Compound Windings. — 
What Alternating Current Is. — Collector Rings. — Cycles. — Alter- 
nating Current Easily Transmitted. — Transformers. — Primary 
and Secondary Coils. — " Step-up" and "Step-down" Transformers. 
— Making a Dynamo. — Novel Power Windmill. — Building a Toy 
Transformer. 

CHAPTER IX 

Electric Motors 194 

Changes of Form of Energy. — A Motor Experiment. — Oersted's 
Discovery. — Electric Engine. — Early Motors. — Paconnoti's Ex- 
periments. — A Simple Motor. — How the Motor Works. — Easily 
Built "Cork" Motor.— Shunt Motor.— Series Motor.— What 
Happens When a Motor Starts. — Alternating-current Motor. — 
Making a Motor. 

CHAPTER X 

The Telegraph 208 

Importance of Morse System. — Joseph Henry and His Experi- 
ments. — What Samuel Morse Did. — First Telegraph Line. — Im- 
provements in Apparatus. — Parts of Telegraph Set. — Battery and 
Lines. — Simple Telegraph Set. — Building Key and Sounder. — 
Relays. — Learning to Telegraph. — Morse Code. — Abbreviations. 

CHAPTER XI 

The Telephone 228 

Vibration and Sound. — Invention of the Telephone. — Bell's Tele- 
phone. — Carbon Transmitter. — How the Telephone Works. — How 
to Make a Telephone. — Microphones. — Induction Coil. — Coils in 
Microphone and Telephone Circuits. 



6 CONTENTS 

CHAPTER XII page 

Wireless Telegraphy 251 

Movement of the Ether. — Hertzian Waves. — How a Message 
Travels. — Receiving Signals. — Aerials. — Simple Receiving Station. 
—Tuning.— A Wave That You Can See.— Tuned Receiving Sta- 
tion Helix. — Tuned Transmitting Set. — Making Wireless Ap- 
paratus. — Building an Aerial. — Insulators. — A Good Lead-in. — 
Figuring Wave Lengths. — "Cat- whisker" Detector. — Silicon 
Detector. — Double-slide Tuner. — Loose Coupler That You Can 
Build. — Fixed Condenser. — Variable Condenser. — Telephone 
Head Set. — Induction Coil. — Transmitting Key. — Making a 
Helix. — Oscillation Transformer. — Simple Helix Clips. — Glass 
Plate Condenser. — Test-tube Condenser. — Sending Transformer. — 
Spark Gaps. — Buzzer Test. — International Morse Code. — A Few 
Wireless Stunts. — Coherer. — Connections for Coherer and Relay. 

CHAPTER XIII 

House Wiring 299 

Importance of Good Wiring. — Methods of Wiring. — Wiring in 

Molding. — Drop Lights. — Service Switch. — Concealed Knob-and- 

tube Work. — Pockets. — Insulators and Cleats. — Tying Wires. — 

Splicing. — Soldering. — Ceiling Plates. — Wiring the Switches. — 

Three-way Switch. — Bringing in Wires. — Circuits in a Large 

House. — Insurance. 

CHAPTER XIV 

Private Electric Plants 318 

Small Plants Perfectly Reliable. — Advantages of Suitable Plant. — 
Types of Plants. — Engines. — Generators. — Switchboards. — An 
Up-to-date Set. — Care of the Plant. — Planning an Installation. — 
Cost of Electric Light. 

CHAPTER XV 

Gas Engine and Automobile Electricity 330 

Principle of Gas Engine. — How Electricity Helps. — Two-cycle 
Engines. — Four-cycle Engines. — Sparks. — Make-and-break Igni- 
tion. — Jump-spark Ignition. — Finding Trouble. — Automobile Elec- 
tricity. — Automobile Power Plant and Wiring. — Ignition. — 
Lighting. — Starting. — Care of Batteries. 

CHAPTER XVI 

Making and Installing Lamps and Fixtures 346 

Lamps Easy to Build.— Simple Shade for Drop Light.— Table 
Lamp.— Shower Fixture. — Desk Lamp.— Piano Lamp.— Installing 
Fixtures. 



PREFACE 



There were once two boys who were neighbors; 
both were about the same age, interested in the same 
things, and one neither any brighter, healthier, nor 
more energetic than the other. The main difference 
was that one lived in a big house and the other in a 
cottage. That is to say, one had spending money in 
plenty, the other had to scrape pretty closely for his 
dimes. 

Their interest in telegraphy resulted in plans for a 
telegraph line between the big house and the cottage. 
Each boy was to supply his own instruments — the 
expense of the lines was to be divided. 

All this was simple for the boy of the big house. 
He bought a sounder, key, batteries, and put aside a 
little money for the line; his end of the work was done. 
For the chum of the cottage every dollar spent meant 
many hours of hard work. He planned for days — 
then bought a few ounces of insulated wire. There 
was hammering and filing and activity in the base- 
ment of the cottage for a week after the instruments 
in the big house were all ready for business. When 
the last joint was soldered and the last screw driven 



8 PREFACE 

home the boys were again equal. The cottage boy 
had made with his own hands the things he needed. 

If you count the labor and thought and planning 
the home-made set required, it cost many times the 
sum paid out for the nicely finished instruments, but 
the roughly made key and magnets were worth the 
highest sum they could be valued at. Aside from 
learning how to build an instrument, the cottage boy 
had learned how to use his hands and his head — the 
boy of the big house learned only how the instruments 
looked, how they were connected, and how they worked. 

The boy of the big house and his chum of the cottage 
are typical American boys; the boy who has things 
done for him and the one who does them for himself. 
It is easy to guess which one has the most fun. How 
much quicker the rainy, stay-at-home days pass by 
for the fellow who always has some interesting piece 
of work on his mind; how much better equipped for 
life's work he becomes. The question of what to do 
with yourself won't come up very often when you 
have a job of magnet winding or battery building in 
the basement or workshop. 

Electricity offers a wonderful field for the boy who 
wants to know its hows and whys. Experiments 
without end can be made with the simplest sort of 
apparatus. With just such cheap material many of 
the greatest experiments have been made, and it is 
certain that fields just as great are still undeveloped. 



PREFACE 9 

As to cost: there are some cases where the expense 
for brand new material will come to more than the 
selling price of a tested piece of apparatus. Insulated 
wire and platinum contacts are not cheap in any sense. 
Even with this in mind, the time and money spent in 
making your own apparatus is well invested. New 
material is not always necessary either, for you can 
secure zinc and carbon from old batteries. They also 
supply good binding-posts. New wire should be used 
where it is at all possible to secure it. So much de- 
pends on this item that taking chances hardly pays. 

In making drawings for the pages of this book the 
idea has been more to illustrate the principle and 
appearance of the finished article than to supply exact 
dimensions. With many of the articles a quarter or 
half an inch one way or the other except on actual 
working parts would hardly matter, so long as the 
parts were made square and fitted well. It is often 
better to use a little ingenuity and apply the material 
you have at hand rather than to try to build exactly 
to some fixed dimensions. 

If through such changes and experiments any 
original apparatus is built by the reader, the author 
will feel more than repaid for the thought and effort 
put into this work. 

You boys who read it, and love, as the writer did at 
your age, to work with tools, may develop into engi- 
neers. Some will desert science to become lawyers, 



io PREFACE 

merchants, and business men, but all are alike in being 
American Boys who will soon be American Men. As 
such you owe to yourselves the trained hands that 
work skilfully with trained minds. This is learning 
that profits in every walk of life. 

Charles H. Seaver. 

Chicago, January u, iqi6. 



American Boys' Book of Electricity 



CHAPTER I 

Magnetism and Magnets 

The magnet is the father of all our modern elec- 
trical apparatus, and it is very old. It is known to 
have been discovered at least 2500 years ago, for in 
585 b. c. a Greek named Thales wrote of the lodestone, 
or natural magnet: "The stone has a soul, since it 
moves iron." This is the first known record of the 
magnet. 

Many scientists put the date much earlier than 
Thales' time. There are many stories of the wonderful 
discovery. One is that when a shepherd named Mag- 
nus was guarding his flocks on the slopes of Mount 
Ida, in Greece, he found that the iron ferrule of his 
staff and the nails in his shoes clung to certain rocks. 
He told of his discovery and showed the stones, which 
were in time named Magnet stones or "Magnets," 
after their finder. A more popular belief is that the 
name at least was taken from the city of Magnesia, 
near which many such stones were found. 



12 



BOYS' BOOK OF ELECTRICITY 



The lodestone about which Thales wrote is an oxide 
of iron called magnetite. It is very heavy, black in 
color, and is now somewhat rare. These stones were the 
only magnets known for centuries. The source of their 
magnetism is even now unknown. The effects were, 
in the dark ages, believed to be wonderful. Lode- 
stones were offered as remedies for gout, rheumatism, 
and many other diseases. Their first real service was 
to make possible the discovery of the compass. 




Fig. i. — An early compass. 

Stories of the compass are as varied as those of the 
lodestone. The Chinese are said to have had one 
variety as early as iooo b. c. This was in the form of 
a little idol turning on a pivot and mounted on a cart. 
The lodestone was fitted in its hand so that the image 
always pointed northward. 

If a compass did exist that long ago it must have 
been forgotten for many years. In 1180, over 2000 
years later, Alexander Neckham, an English monk, 
wrote the first description of the mariner's compass. 



MAGNETISM AND MAGNETS 



13 



The first real compasses were made of iron needles 
thrust through bits of wood, and floated in vessels of 
water. These were' only used on shipboard when the 
weather was cloudy or foggy, so they were plainly not 
very reliable. The needles were not permanently 
magnetized, and had to be rubbed with a lodestone 
each time they were used. 




Fig. 2. — Card of mariner's compass. 

From these crude compasses the terms north pole 
and south pole originated, as used with a magnet. 
By north pole we mean the north-pointing pole, and by 
south pole, the south-pointing pole. Every lodestone 
and every magnet, whatever its shape, must have these 
two poles. 

As in other electrical devices, there has been a great 
improvement in nautical compasses. Modern ones 



14 BOYS' BOOK OF ELECTRICITY 

are delicately balanced, and are hung so that they are 
always level no matter how the ship may roll. In 
these the magnet is not visible, for it is covered by the 
compass card, marked with all the divisions. As the 
card is carried by the needle it indicates directly every 
point of the compass. 

Even these perfect instruments do not point exactly 
north, for the magnetic poles of the earth are not at 
the geographic north and south poles. The magnetic 
north pole is really about 1400 miles south of the 
geographic pole; so the compass needle of a ship is 
seldom pointing due north. There is a line, however, 
along which the compass is correct. This is called the 
Agonic line. In the United States it passes through 
Charleston, S. C, Columbus, O., and Lansing, Mich. 
In these and the other points on the Agonic line the 
compass is correct. 

The location of the Agonic line is not permanent, for 
the magnetic pole is constantly moving. This move- 
ment is carefully watched by the government, so that 
proper allowance may be made. A full movement of 
the pole takes about 320 years. 

The compass has another motion. This is magnetic 
dip. If you were to start at the equator with a per- 
fectly balanced compass, free to swing up and down 
instead of around, you would find that it tipped as 
you came near the magnetic north pole. This dis- 
covery was made by an Englishman named Robert 



MAGNETISM AND MAGNETS 



i5 



Norman, who described it in 1576. The unbalancing 
pull on the mariner's compass is now taken care of by 
a sliding weight on the frame which carries the needle. 

EXPERIMENTS WITH THE MAGNET 

A horseshoe or bar magnet will enable you in a few 
minutes to gain at first hand the knowledge which the 




SjJ 



Fig. 3. — Horseshoe magnet and bar magnet. 

discoverers were centuries in collecting. One of these 
can be bought at any toy store. For our purposes the 
bar magnet is better, as the poles are separated. 



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Fig. 4. — Magnetizing a needle. 



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",\VV' 



Fig. 5. — Needle and iron filings. 



Rub a large steel needle with one pole of the magnet; 
a knitting needle or darning needle will do. Rub 



16 BOYS' BOOK OF ELECTRICITY 

only one end, and always stroke away from the center. 
After a dozen strokes or so bring the needle near to 
some iron filings. Two things are at once apparent: 
First, you have made a magnet attracting equally at 
both ends; second, the pull is much stronger at the tips 
or poles than anywhere else. 

Now put this same needle through a cork, and let it 
float in a large china or glass dish of water. When it 
comes to rest it will point north or, rather, to the north 
magnetic pole. This is the early form of compass. 
The pole pointing north is the north-seeking pole, the 
opposite one the south-seeking pole. 

Bring your magnet toward the needle, and the bal- 
ance is at once disturbed. One end of the needle will 
follow the magnet. Reverse the magnet and the 
needle turns end for end. If the pole you brought 
toward the needle was the south pole, the needle's 
north pole was attracted. Unlike poles always at- 
tract; like poles repel. This was one of the greatest of 
the early electrical discoveries, and was mentioned by 
Dr. Gilbert, who was Queen Elizabeth's physician, 
and who made many electrical experiments. 

Robert Norman's experiment showing magnetic 
dip may be easily performed just as done by its orig- 
inator. Cut out a ball of cork as nearly round as 
possible, and large enough to float a darning needle. 
Run the needle through until it just balances. Then 
cut the cork down bit by bit until it just floats the 



MAGNETISM AND MAGNETS 



17 



needle. If too much is taken off add a teaspoonful 
of salt and it will float again. Now magnetize the 
needle by rubbing it with the magnet. The needle 
does not float evenly now; its north pole tips toward 
the earth's north magnetic pole. 

This same floating needle will show the attraction 
of unlike poles, and the repulsion of like poles. A 
fish made from a cork, with the needle entirely hidden 




Need le 



N 




Fig. 6. — Robert Norman's experi- 
ment. 



5tiol 
Fig. 7. — Fish cut from cork. 



and a few shot to weight it down, seems almost as active 
as if it were alive. 

Attraction becomes much stronger as the magnet is 
brought nearer to a piece of iron or steel. At 6 inches 
from the floating needle or magnetic fish the attraction 
would be slight. At 3 inches it would be four times 
as great, and at 1 inch thirty-six times as great. 

Neither the glass nor the water makes the slightest 



i8 



BOYS' BOOK OF ELECTRICITY 



difference in this attraction. To illustrate this in 
the Norman experiment, lay your bar magnet on a 
book about 2 inches away from the needle. The 
needle tips toward the magnet. Now place a piece of 
wood, glass, or paper between magnet and needle. 
There is no change in the inclination. Now put a 
piece of tin or iron in place of the other substance. 




Fig. 8. — Showing how lines of force pass through glass. 

At once the dip becomes less. The magnetism has 
been screened by the iron. 

This screen effect is used in many ways. Watches 
carried in power stations are sometimes made with an 
inner case of soft iron. Instruments to which mag- 
netism would be harmful are inclosed in iron boxes. 

Attraction and repulsion can be well shown also by 
bringing a magnet near a suspended needle which has 
been magnetized. 



MAGNETISM AND MAGNETS 



19 



By putting pieces of glass or books between magnet 
or needle you will see that the action is the same 
whether they are there or not. 







Fig. 9. — Attraction and repulsion. 



MAGNETIC FIELD 

As the magnet need not touch the needle to influence 
it, you can see that there must be something which 
reaches out and does pull or push the needle around. 
The strength of a magnet is said to be in the "field of 
force" that surrounds it. This field is made up of 
countless invisible lines of force. 



20 



BOYS' BOOK OF ELECTRICITY 



Anyone can trace these lines easily with the help of 
a few pinches of fine iron filings. 

To do this lay a clean piece of cardboard over the 
magnet, dust the filings on it, and then tap the card- 
board gently with your finger. By trying this experi- 
ment with the magnet in several positions you can form 
an excellent idea of just the way the lines are arranged. 
These are the lines that attracted and repelled the 




Fig. 10. — Magnetic field of bar magnet. 

needle. They pass through wood, paper, lead, and 
practically every substance but nickel and iron as 
freely as rays of light go through a window-pane. 

A sheet of iron placed near the magnet offers such 
an easy path to the lines that they do not reach be- 
yond it at all. The sheet of iron, however, becomes 
slightly magnetized. This is called magnetism by 
induction. A good example of this sort of magnetism 



MAGNETISM AND MAGNETS 



21 



can be shown with a few small tacks. Arrange six or 
seven tacks end to end in a row, and the magnet will 
pick them all up. A temporary magnet has been 




Fig. ii. — Magnetic field of horseshoe magnet. 

made of each tack. It carries the lines of force to pick 
up the next in the chain. 

A magnetized needle free to move in all directions 
always takes a position following the lines of force as 



22 



BOYS' BOOK OF ELECTRICITY 



closely as possible. This can be proved by laying a 
pocket compass on the piece of cardboard where the 
iron filings have been allowed to follow the lines. If 




Fig. 12. — Field at poles of same horseshoe magnet. 

the magnetized needle was very short and perfectly 
free to turn in any direction it would be possible to 
draw a map of the magnetic field of any magnet. 




Fig. 13. — Magnetism by induction. 

This would correspond quite closely with the one ob- 
tained by the filings. 

It was through the action of iron filings that an 
Italian named Cabaeus first discovered the lines of force 



MAGNETISM AND MAGNETS 23 

in 1629. He called thent the "magnetic spectrum." 
The idea of lines came to him because the fine iron 
filings stood like hairs on the poles of the lodestone. 
He believed them to be straight, instead of curved from 
pole to pole as the cardboard experiment shows. 

The earth itself is a big, but weak magnet. Its lines 
of force stretch 4000 miles unbroken, but have only- 
enough strength to turn a delicately poised magnet or 
compass needle. Since opposite poles attract, it seems 
strange that the north pole of the needle points to the 
north magnetic pole. In reality, the proper naming of 
the north-pointing tip would be the south pole. But 
the tips were named before anything was known of the 
attraction of unlike poles. To avoid confusion, espe- 
cially among sailors, the north-pointing pole has always 
been called the north pole. 

MAGNETIC MATERIALS ** 

Permanent magnets are all made of tempered steel. 
Something in its structure enables it to hold the mag- 
netism. Soft iron will stay magnetized only a very 
short time. 

Scientists explain this difference by a peculiarity of 
the molecules in the two metals. The molecules are 
the very small particles of which the metals are made 
up. For convenience we will imagine them large 
enough to be seen. In unmagnetized iron or steel 
they point in all directions. 



24 



BOYS' BOOK OF ELECTRICITY 



Bring a magnet near to a bar of iron, and every 
molecule swings toward it as so many compass needles 
would. Each molecule has a north and south pole. 
Every one is magnetized by induction. The north 



i^?^^^y^ 



Fig. 14. — Effect of magnetism on iron or steel bar. 

poles are all pointing in one direction and the south in 
the other. Take the magnet away and all the par- 
ticles swing back helter-skelter. The bar loses its 
magnetism quickly. 

The molecules in a bar of hardened steel are stifTer. 
They turn with difficulty. If the steel is the right kind, 
and time is given to rubbing it with a magnet pole, the 
molecules are in place to stay, and will not swing back 



£ 



5 



N S 



fl l" s( 



Fig. 15. — Many magnets could be made from one. 

unless the bar is heated or jarred. These little mole- 
cules are so firmly fixed in a good bar magnet that it 
could be sawed in a dozen pieces, and each one would 



MAGNETISM AND MAGNETS 25 

have a north and south pole, just as the unbroken bar 
did. 

A simple comparison of materials may be made by 
rubbing first a piece of soft iron wire and then a steel 
knitting needle with one pole of a magnet. Be sure to 
rub always in one direction — away from the center, 
and with one end of the magnet. Now dip the iron 
wire in the filings and you will find that only a few 
cling to it; a good many more will be picked up by the 
steel needle. Half an hour later the iron wire will have 
lost all its magnetism, while the steel needle will be as 
good as ever for a long time. 

Although steel makes the best magnets, it is not the 
only magnetic material. It offers a very easy path to 
the magnetic lines and is called Paramagnetic. Other 
Paramagnetic metals are nickel, cobalt, and manganese, 
but they are all so far below steel that no use is made 
of their magnetic quality. Metals offering resistance 
to the magnetic lines of force are called Diamagnetic. 
Phosphorus, bismuth, zinc, and antimony are all 
Diamagnetic. 

To make a permanent magnet from a bar of steel 
first make sure that the bar is tempered to the proper 
hardness. This can be decided by testing it with a 
file. If the file cuts it easily the bar should be heated 
to a red heat and dropped into water. This will make it 
very hard. When cooled, lay the bar on a table and rub 
one end with the north pole of a strong magnet. The 



26 



BOYS' BOOK OF ELECTRICITY 



opposite end should then be rubbed with the south pole. 
Always rub in one direction — away from the center. 

To preserve the magnetism in this or any magnet 
care should be taken to protect it against several 
things known to destroy magnetism. Never pound or 
hammer a magnet. To guard against rust the bar 
should be painted or shellacked within J inch of each 
end. It has been found that most of the magnetic 
effect is in the outer surface of the bar. When the 
surface is pitted with rust or eaten with acid most of 
the magnetism is lost. 



Soft 
Iron 
Keeper^ 




Soft 
Iron 



HU/v^ Keeper 



Fig. 16. — Pair of bar magnets with " keepers " in place. 

Horseshoe magnets are usually furnished with a 
piece of soft iron called a keeper. This should always 
be kept in place when the magnet is not in use. It 
furnishes an easy path for the magnetic lines between 
the poles and in some way retains the strength of the 
magnet. 

Bar magnets should be kept in pairs. They should 
be put side by side with a thin strip of wood between. 
The north pole of one should be near the south pole of 
the other. A keeper of soft iron put at each end of the 
pair of bars retains the magnetism just as the single 
keeper does in the case of the horseshoe magnet. 



CHAPTER II 

Static Electricity 

"Static" is a word derived from Greek, meaning 
to stand, or remain motionless. Static electricity 
is really standing, or motionless electricity. It might 
well be called "universal" electricity, for it is every- 
where. There is static electricity on the trees, the 
grass, the piece of paper you pick up, the book you are 




Fig. 17. — Attracting bits of paper with electrified sealing wax. 

reading. This common form of electricity escapes our 
notice because the amount is usually so small. Some 
action is necessary to draw it to our attention. 

An extra accumulation of electricity is easily caused 
by rubbing. Rub a hard rubber comb on your sleeve 

and you will find that it picks up bits of paper just as 

27 



28 BOYS' BOOK OF ELECTRICITY 

the magnet attracts pieces of iron. Every boy has 
noticed the sparks that come from rubbing a cat's fur 
when the cat is dry and warm. Here the accumula- 
tion of static electricity is marked both by an attractive 
effect, for the hairs rise to meet your hand, and by a 
slight crackling noise. If dark enough there is a third 
result. This is the appearance of small sparks. 

It was from the simple attractive effect that the word 
electricity came. Elektron is the Greek word for 
amber, with which the strange attraction was first 
noticed. Amber is petrified resin, and is used now for 
pipe-stems, beads, and ornaments. It is found now 
mainly on the shores of the Baltic Sea. 

Probably the electrical properties of amber were 
known long before lodes tones were discovered. The 
Greeks loved jewelry, and the beautiful sunlike amber 
was used as a head ornament thousands of years ago. 

In Syria women used amber spindles on their spinning 
wheels. They noted its attractive quality early. 
When their spindles turned they seemed not only to 
grasp bits of wool, but to hold them fast. From this 
property came the Syrian name for amber. They call 
it "harpaga" which means "the clutcher." 

Static electricity has not a general use. Its great 
value has been in the promotion of experiments, and in 
creating interest in electrical matters. The many 
laws discovered are of use in helping us to make proper 
devices to protect machines and property, even life, 



STATIC ELECTRICITY 29 

against the effects of static electricity. The one great 
use of this form of electricity is in the operation of the 
Trans-Atlantic cables, which have become somewhat 
less important since the perfection of wireless 
telegraphy. 

The little sparks seen on a dry day after one's feet 
are shuffled along the carpet are quite different from 
the ones visible at night when the trolley pole of a 
street car strikes a joint in the wire. They are both 
electricity, it is true, but one is the static form, while 
the other is always in motion. There is a relation be- 
tween the two, but static only plays, while "current" 
electricity is the everyday worker. 

At first the relation between magnetism and static 
electricity was thought to be very close. Experi- 
menters held that both magnet and amber acted alike, 
except that the magnet received its power from the 
Arctic regions, while that of amber come from the 
Antarctic. It was not until Gilbert's time that elec- 
tricity was found to be present in other materials. 
The idea before that was that amber alone would 
attract light materials when rubbed. Gilbert found 
that sulphur, glass, resin, diamond, and many other 
materials had the same property. This astonishing 
discovery was the first step toward the electrical 
science of to-day. 

Gilbert's first instrument was a light pivoted needle. 
It showed the attraction of amber and the other sub- 



3Q 



BOYS' BOOK OF ELECTRICITY 



stances by turning strongly when brought near to 
them. A needle of this sort can easily be made from 
a slip of paper folded and supported on the point of a 
needle. When a rubbed piece of glass or rubber is 
held near it, it behaves much as the compass needle 
did. This is a simple " paper electroscope." 

Gilbert is often called the father of electricity. 
After his experiments, trials with rubbing glass and 



Fold 



/ 



^Fold 




Fig. 18. — Paper electroscope. 

drawing sparks became almost a craze in England, 
Europe, and even America. Nearly 140 years later 
the discovery was made in France by Dufay that there 
were really two kinds of static electricity. It was found 
that a rod of amber or resin hung from a string was 
pushed away when another piece of rubbed amber was 
brought near. When a piece of rubbed glass was 
brought near there was a strong attraction. One kind 



STATIC ELECTRICITY 



3i 



of electricity was called resinous; the other vitreous, or 
glassy. 

With a glass rod made in something the same way as 
the little paper needle, the difference between these 
two electricities can easily be seen. The glass rod 
should be 6 or 8 inches long. First balance it care- 
fully to find the center; then cut through one side with 
a small three-cornered file. Now the tube can be 
pivoted on a needle stuck in the cork of a dry bottle. 




Fig. 19. — Repulsion of like charges. 

When a piece of sealing wax is rubbed and brought 
near, the rod is attracted. If a glass tube is then 
rubbed and brought near, the pivoted tube swings 
away. In modern terms the glass rod is said to be 
"positively" electrified, while the wax is "negatively" 
electrified. 

The balanced rod shows that like charges repel and 
unlike ones attract, in just the same way as the like 
and unlike poles of the magnet behaved. 



32 BOYS' BOOK OF ELECTRICITY 

The rod need not touch the needle to attract or repel 
it, and the needle is itself magnetized merely by the 
approach of the electrified body. This discovery was 
made by an Englishman named Gray in 1728. He 
found that an electrified body made another body 
electric by induction, and that all materials could be 
electrified in this way. Even red-hot coals behaved 
like amber. To be charged, however, the material 
must be supported or hung by an insulating material. 
Glass, mica, silk, paper, and such materials he found to 
be insulators or non-conductors, while all metals are 
conductors. 

Gray's materials were at first even simpler than 
most boys can now have. Bits of twine, glass, resin, 
tin, and such material made up his whole "laboratory." 
They were enough to prove that a conductor actually 
carried electricity. He tried his experiment with a 
long piece of twine, which was a conductor, supported 
by silk thread, which is an insulator. Another experi- 
menter in Germany tried to see how fast the charges 
traveled. He supported a long loop of string by silk 
threads and charged one while he watched the other. 
A few pieces of gold leaf put at the far end of the cord 
were to indicate when the charge had traveled the 
length of the string. After many tests he announced 
that the movement was instantaneous. Little wonder 
that Gray formed this opinion from his crude appa- 
ratus, for the charge travels with exactly the same 



STATIC ELECTRICITY 33 

speed as light. The exact figure is 186,213 miles per 
second. In a single second, then, a flash of electricity 
could go around the world seven times. 

About thirty years after the discovery of the two 
kinds of electricity came one more wonderful still. 
Benjamin Franklin startled the world by proving that 
the sparks made in his laboratory were exactly the 
same as lightning. His experiment was as wonderful 
as it was dangerous. Several scientists had already 
ventured that lightning and electricity were the same, 
but none had thought of a way to prove the belief. 
The French came nearest with a tall iron rod which 
gave off sparks during thunder storms. Beyond doubt 
the rod became electrified during thunder storms, but 
as it did not reach even the lowest clouds there was no 
proof that the sparks they received were actually 
lightning. 

Franklin had thought of this experiment even before 
it was tried in France. For his plan a high steeple was 
necessary; and there was not even a church steeple in 
all Philadelphia. An idea bolder than his first came 
to him. He could reach the very heart of the cloud 
with an ordinary kite. If lightning was electricity 
the cord would become charged. 

The kite that Franklin flew was made of two light 

strips of cedar with a thin silk handkerchief stretched 

across and fastened at the corners. At the top of the 

upright was a sharp wire about a foot long. The cord 

3 



34 BOYS' BOOK OF ELECTRICITY 

was ordinary twine, but to this was fastened a piece of 
silk ribbon and a key. As silk is an insulator it would 
give some protection, while the conducting key would 
serve to draw sparks from — if sparks came. 

With his only son, a young man of about twenty-two 
years of age, he went out into an open field in a gather- 
ing storm. The wind came in gusts, and the rain began 
to fall while they were preparing the kite for its trial. 
Lightning flashes from the dark low clouds came nearer 
and nearer. The kite was wet and rose sluggishly in 
the fitful wind. With thunder crashing around them, 
and drenched by the rain, Franklin and his son went 
under a shed for protection. The kite had disappeared 
in the cloud and the mist. The critical point of the 
test was near, and both watched cord and key. Sud- 
denly they saw the little loose fibers of the string sepa- 
rate themselves from the kite cord and each stand 
erect. The time for the trial had come. Franklin 
put his knuckle near the key. As his hand came near 
the metal there came a crackling sound. A little spark 
jumped across the gap. It was the same little spark 
in every way that he had seen in his laboratory thou- 
sands of times. His experiment was successful and his 
name immortal. Lightning and electricity were the 
same. 

This discovery was then considered the end of elec- 
trical knowledge, as the last secret had been solved. 
As we now know, it was only the beginning. 



STATIC ELECTRICITY 35 

APPARATUS FOR EASY EXPERIMENTS 

With the three pieces of apparatus described many 
experiments can be made. These are the Electro- 
phorus, the Electroscope, and the Leyden Jar. The 
sparks secured will not be large, but will permit a 
study of static electricity. 

THE ELECTROPHORUS 

Melt enough resin and sealing wax, using two-thirds 
resin and one- third sealing wax, to fill a large pie tin. 
This mixture should be melted in a tin cup held in 
boiling water; if held over a flame it is apt to catch 
fire. When thoroughly melted and mixed pour it in 
the tin and allow it to cool slowly. 

In the center of another pie tin about 2 inches smaller 
solder a flat-headed brass wood screw, which has first 
been screwed into a wooden plug as shown in the dia- 
gram. This plug should be whittled to fit tight in the 
neck of a bottle. An ordinary pint milk bottle will 
serve very well. If desired the plug can be coated 
with shellac and the bottle put on to dry in place. 
The electrophorus is now complete. You have made 
a simple machine for generating static electricity. 

To use the electrophorus first rub the resin briskly 
with a piece of flannel. Then take the small tin by 
its glass handle and set it gently in place on the resin 
cake. Now touch the two tins at once with the thumb 
and finger of one hand. Lift the small tin again by 



36 



BOYS' BOOK OF ELECTRICITY 



its glass handle. On touching the pan a small spark 
is seen. 

The action you have caused is this: First, the sur- 
face of the resin was charged negatively by rubbing, 
and the positive charge was driven into the metal 
pan. Second, the smaller pan was electrified by in- 
duction when placed on the resin cake. The tin does 
not rest evenly on the resin, but touches it at thou- 




i^iVt'> vvv'i -Vff >: r - vr-arv^sg- 



Fig. 20. — A "pie-tin" electrophorus. 



sands of little points. This contact is so light that the 
negative charge does not escape to the upper tin. On 
the contrary, it induces a positive charge on the lower 
surface of it and drives the negative electricity to the 
upper surface. Touching the two tin plates with 
thumb and finger allows the negative charge to escape 
to the bottom tin and the earth. The positive charge 
is held, and cannot escape, When the plate is lifted 
it is positively charged. 



STATIC ELECTRICITY 



37 



This charging may be repeated many times without 
rubbing the resin again. 

THE LEYDEN JAR 

The only material needed to make a Leyden jar is 
an ordinary jar of good clear glass, some tin-foil, a piece 
of brass curtain rod, a small brass knob, and a piece 




Fig. 21. — Leyden jar. 




22. — Cover of jar, showing rod 
with chain attached. 



of chain. Before starting, the jar should be thor- 
oughly washed and dried. The inside should then be 
coated with shellac. While this is drying the inside 
tin-foil can be put in place. This tin-foil lining should 
extend clear around, coming within 3 inches of the top, 
and lapping over the bottom \ inch. The bottom piece 
of the lining should cover the bottom of the jar well. 



38 BOYS' BOOK OF ELECTRICITY 

Shellac and tin-foil can now be put on the outside 
in just the same way. The cover should be made 
from a well-dried piece of board, and must fit tight. 
Bore a hole in the center of the cover just big 
enough to force the rod in. At the top of the rod 
solder or screw the ball. At the bottom fix the chain, 
which should be long enough to rest on the tin-foil 
fining. Before putting the cover on dry out the jar 
thoroughly. Then see that the cover fits tight, shellac 
it well, and put it in place. The jar should be practi- 
cally air tight. 

You now have a device for storing static electricity 
in small amounts and for a short time. 

DISCOVERY OF THE LEYDEN JAR 

The Leyden jar is named for the town of Leyden, in 
Holland, where the discovery was first made that 
static electricity could be stored and held for a short 
time. Peter van Musschenbroeck accidentally hit 
upon it in 1746. His apparatus was a gun barrel 
suspended by silk threads, and included a piece of 
brass wire and a glass jar partly filled with water. 
The wire extended from the gun barrel into the water. 
The bottle was held in his hand. A static machine 
worked by two assistants supplied electricity to the 
gun barrel. Expecting to draw a small spark from 
the wire the experimenter touched it. The spark 
came, but was stronger than had ever been made 



STATIC ELECTRICITY 



39 



before. The water in the jar acted as the tin-foil lining 
does, while the hand supplied the outer conductor, and 
the experimenter received the full force of the shock 
through his body. The spark that nearly knocked the 
experimenter senseless made the name of his town 
common in electrical science. 



THE ELECTROSCOPE 

Any instrument which shows the presence of static 
electricity is called an electroscope. The pivoted 




Fig. 23. — Pith-ball electroscope. 



Electroscope with two 
pith balls. 



paper needle was the simplest kind possible. A much 
better one can be made from a bottle and a ball of 
pith. The bottle should be clean and dry, and should 
have a cork. In the cork insert a wire bent as shown. 
From the tip hang a silk thread with the pith ball on the 
end. 



40 



BOYS' BOOK OF ELECTRICITY 



With this many tests may be made. Bring the cover 
of the electrophorus near and the ball is attracted 
strongly. Let the ball touch it and it is repelled. 
This illustrates the attraction of unlike charges and the 
repulsion of like charges. 

Now hang two pith balls by silk threads of the same 
length, charge the cover of the electrophorus and 



Glass Tube 
Brass Rod 




Fig. 25. — Gold-leaf electroscope. 

bring it near. Both balls are charged negatively by 
induction. As they are charged alike they repel each 
other. On this principle the gold-leaf electroscope 
works, though it is much more delicate. 

The gold-leaf electroscope can be made from any 
wide-mouthed bottle or fruit jar that can be provided 
with a tight-fitting cork. Besides the bottle the mate- 



STATIC ELECTRICITY 41 

rials needed are: a brass tube or rod; a glass tube large 
enough to slip this through; a brass knob, and two pieces 
of gold or aluminum foil. The foil is simply very 
thinly beaten metal, and may be obtained from al- 
most any sign painter. 

First bore a hole through the cork with a small 
rat-tail file so that the glass tube will fit tight. The 
tube should extend an equal distance above and 
below the cork, and should come to within 3 inches 
from the bottom of the jar when the cork is in place. 
The tube can be cut by notching it with a three- 
cornered file and then hitting it a sharp tap. Solder 
or screw the brass knob to one end of the brass tube. 
Then slip the rod through the glass tube. It should 
be cut so that only J inch extends at the bottom. 
This end should be flattened by pounding. Now tip 
the tube up and pour shellac in so that the tube and 
rod will be held firmly together when it dries. After 
the drying is complete scrape the flattened end of the 
rod clean and fasten the two pieces of leaf in place. 

As the electroscope must be kept dry to work 
properly, it is a good plan to heat the bottle before 
finally putting the cork in. To make a good piece 
of work the cork should also be well shellacked. A 
little calcium chloride dropped into the bottle will 
absorb any moisture that might remain or leak in. 
This must be fresh. Buy the calcium chloride the 
day you are going to finish your electroscope. 



42 



BOYS' BOOK OF ELECTRICITY 



THE DISCHARGER 

The Leyden jar should always be discharged by a 
metal instrument called a discharger. This can be 
made from a piece of heavy wire and a bottle. Twist 
the wire together for about 2 inches; then spread the 
ends out as shown. A brass knob or plate should be 
soldered to each tip. The twisted end can now be 
inserted in the neck of a bottle, and the discharger is 




Fig. 26. — Discharger for Leyden jars. 

complete. To discharge a jar, bring one of the tips in 
contact with the brass knob and touch the other to 
the tin-foil coating. 



CYLINDER ELECTRIC MACHINE 

Secure a good clear glass bottle about 4 inches in 
diameter and 8 or 10 inches long. See that it is round 
and that the sides are straight. Clean it carefully; 
then roughen the bottom at the center a little with a 
piece of emery paper. Find the exact center with a 



STATIC ELECTRICITY 



43 



compass or by means of a circle marked on a piece of 
paper. With a glass-cutter make a hole in the bottom 
about \ inch in diameter. Smooth the edges with a 
file. In as near the exact center of the bottom as 
possible cement a large spool. Either bichromate 



Oiled <5,lh 



Collector 



a Coated 
th 




^. Brass Tacks 



yA. 



Sola 
Joi 



^B 



Bran Tube ** n f* 
Collector 



Friction Block 




o 



Section of Friction Pad 

Fig. 27. — Cylinder electric machine. 



O 



;□ 



% 



Conductor 
Mounted on 
Insulating 
Post J 



s^JZk 



glue or a good china cement can be used for this pur- 
pose. In the neck of the bottle fasten a spool of the 
same kind as the one in the bottom. This should be 
whittled or turned down carefully so that the hole 
will not be thrown out of center. The cylinder is now 
ready for the axle. For this a piece of hard wood can 



44 BOYS' BOOK OF ELECTRICITY 

be used. It should fit tight in the spools, and can be 
cemented in place with shellac. 

The bearing pillars should be of good dry, clear 
wood. 

As the action of this machine depends on friction, 
the block which rubs the glass is especially important. 
This block should be made a little shorter than the 
bottle, and hollowed out to fit the curvature of the 
side. It is held in place by wood screws. Before 
being fastened to the standard, however, it should be 
wrapped with four layers of flannel and two of silk. 
These should be wrapped on tightly and fastened with 
small tacks. 

On the opposite side of the bottle the electricity is 
collected from the glass by a set of small sharp points. 
From the points it is conducted to a brass ball, where 
the Leyden jar is charged or sparks may be drawn out. 

In making the conducting part of the cylinder 
machine the ball, brass tube, and brass strip should 
first be soldered together. A f-inch tube is a con- 
venient size to handle, and the strip can be of that 
width and any thickness available. The ball can be 
a little larger than the tube. In soldering these to- 
gether be careful to clean them thoroughly, and tin 
the surfaces to be fastened together. The side to be 
nearest the cylinder should be tinned completely. 
Tinning is simply applying a thin coat of solder over the 
brass, and makes the soldering much easier. 



STATIC ELECTRICITY 45 

After the ball, tube, and strip have been soldered 
firmly together, the collecting points should be soldered 
to the strip. These points may be made either from 
brass-headed tacks or small brass screws. If screws 
are used the threads should be smoothed down and 
the points sharpened. Then the flat head of each 
screw should be tinned. Solder them onto the strip 
one at a time, and as close together in line as their 
heads will permit. Be sure that each point in the row 
is of the same length. 

The conductor is now ready for its glass tube sup- 
port. This should be of about the same size as the 
tube, and long enough to bring the collecting points 
even with the center of the cylinder. A wooden 
plug curved to fit the brass may be cemented to it, 
and fixed in the top of the tube. Another plug fas- 
tened by a screw to the wood base makes a firm sup- 
port for the tube. When in place the collecting points 
should not be more than -^ inch away from the 
cylinder. 

A shellacked or oiled-silk curtain should now be 
made, and tacked to the top of the rubbing block, so 
that it will lay on the top of the cylinder and extend 
to within \ inch of the collecting points. 

Sparks secured with this machine are much stronger 
if the friction cushion is coated with mercury amalgam. 
This is made by mixing melted zinc and tin with 
mercury. The proportion is 2 parts of zinc, 1 of 



46 BOYS' BOOK OF ELECTRICITY 

tin, and 6 of mercury. First melt the zinc, and to 
this add the tin. While cooling, pour in the mercury ? 
being very careful not to breathe the fumes, as they 
are poisonous. Pour the mixture into a wooden box 
and shake until cool. The amalgam should be 
powdered and mixed with lard before being applied 
to the cloth cushion. 

The machine should now be in working order and 
will produce a spark at the brass ball when the cylinder 
is rotated. A crank can be arranged for this purpose 
as shown in the illustration, although much longer 
sparks can be secured if a pulley can be fitted and a 
small motor used. 

A FEW STATIC EXPERIMENTS 

With the gold-leaf electroscope static charges may 
be detected in many unlooked-for places. The ways 
of exciting these little charges are almost endless. 
Sharpen a lead pencil and hold it near the ball of the 
electroscope. The delicate gold leaves will separate. 
Tearing a piece of paper, blowing powdered chalk 
from a pair of bellows, all have the same effect, showing 
that the rubbing or friction has caused an electrical 
disturbance. Pound a little dry brimstone in a mortar 
and let it fall on the brass ball. It is charged enough to 
cause separation of the leaves. Let another boy stand 
on a small board supported by four heavy glass 
tumblers, and then place his finger on the knob of 



STATIC ELECTRICITY 47 

the electroscope. No disturbance is visible. Flap 
him with a silk handkerchief and the leaves spread 
apart. 

Care should be taken to guard the gold-leaf elec- 
troscope against heavily charged bodies, such as the 
electrophorus, as the force would tear apart the deli- 
cate gold leaves. 

An experiment sometimes called the "electrified frog 
pond" is easily performed with the electrophorus. 
After the resin cake has been rubbed with a flannel 
cloth, place several bits of paper around the edge. 
Now touch the edge of the upper plate and lift it by 
the insulated handle. The bits of paper will jump 
from the edge of the pan in a very lifelike manner. 
Green paper cut in the shape of frogs can be used to 
make the action seem even more real. This experi- 
ment is another example of the repulsion of like 
charges. As soon as the pieces of paper become posi- 
tively charged from the pan they are actually lifted off 
and pushed away. 

A very well-made Leyden jar could be charged by 
the tiny spark of the electrophorus. With an ordinary 
jar the method is not practical, and the larger spark of 
the static electric machine must be used. To charge 
a jar with the machine described, bring the collecting 
knob near the brass knob of the machine, holding the 
jar by its tin-foil coating. When the glass cylinder is 
turned by its crank, a small crackling spark will be 



48 BOYS' BOOK OF ELECTRICITY 

seen to jump across the gap. When this spark stops 
the jar is charged to its full capacity. 

In this state the inside coating generally has a posi- 
tive charge, while the outside is charged negatively by 
induction. The charges are equal and opposite. If 
the jar is placed on an insulating glass it will not 
charge, as the necessary negative charge cannot accu- 
mulate from the earth on the outer coating. The 
table or floor is a fairly good conductor. If the outer 
coating is connected to a water-pipe, a better charge 
than ever can be obtained. 

For discharge a complete circuit is also necessary. 
The discharger should be used, touching one tip to the 
tin-foil coating and the other to the brass ball. 

As the discharger tip comes near to the ball, a spark 
jumps across the gap. The charges have been equal- 
ized. Now recharge the jar, and place it on a clean 
pane of glass supported by four tumblers. When the 
ball is touched, a much smaller spark than before is 
seen. A similar spark can now be taken from the 
coating, another from the ball, and so on until the jar 
is discharged. 

By connecting several jars together a much larger 
spark can be obtained. There are two kinds of con- 
nections possible. These are called the "series" con- 
nection, and the "parallel" connection. A combina- 
tion of these can also be made. 

The series arrangement as shown consists in con- 



STATIC ELECTRICITY 



49 



nee ting the tin-foil coating of one jar with the metal 
knob of the next. By this means the voltage is in- 
creased and a longer spark secured. All of the jars 
but the last one must be set on insulating stands. 




Fig. 28. — Series connection. 

The parallel connection can be made by letting all 
the jars stand on a strip of tin-foil and connecting all 




Fig. 29. — Parallel connection. 

the knobs by a small wire. This arrangement in- 
creases the size of the spark, but not its length. 

If desired, several jars can be wired in series groups 
and the groups wired in parallel. 



So BOYS' BOOK OF ELECTRICITY 

Especial care should be taken with either of these 
arrangements not to let the jars discharge through the 
body. Do not play jokes with static electricity. 
The shock is not only unpleasant, but apt to be very 
harmful. In spite of the supposed value of electric 
treatment for nervousness, its helpfulness is very 
doubtful. Common sense demands the use of a dis- 
charger whenever a large jar or a series of any size is 
to be discharged. 

Spark experiments done in a darkened room can 
be made to give a very brilliant display. Metal 
filings put in the path of the discharge from two or 
three jars make a long bright spark possible. These 
filings should be scattered over the surface of a glass 
plate which has been bound at two edges with tin- 
foil. One edge should touch the coating of the jar; 
one tip of the discharger should then be placed on 
the opposite edge, while the other tip is brought near 
to the brass ball. A bright zigzag spark will flash 
across, burning the filings in its path. Several kinds 
of metal can be tried. The color of the flash will 
be different for each. 

Paper can be punctured with the spark from a 
Leyden jar by holding it across the path of the spark. 

Although static electricity is not easily turned 
to power use, a small static motor can be made in a 
few minutes' time. All that is needed is a bottle 
and a piece of copper wire. Cut off two pieces of 



STATIC ELECTRICITY 



Si 



wire each 2 inches long and flatten them at the middle. 
Solder them neatly together in the form of a cross. 
Then file each end to a sharp point. Turn them 
back so that they all point in the same direction, 
and bend each down a little. Where the wires cross 
make a dent with a sharp punch. The wheel is 
now ready to balance on a needle stuck in the cork 
of an empty bottle. Connect the needle with the 
prime conductor of the static machine, and turn 




7b Conductor 




' Fig. 30. — Burning metal filings. 



of Static 
Machine 



Fig. 31. — Static electric motor. 



the crank. Static discharge from the sharp points 
of the wheel into the air will cause the wheel to turn. 
The spark from a static machine can be broken up 
in a pretty display by means of a tin-foil spark pane. 
Take a pane of glass 3 by 4 inches in size, shellac 
one side and paste on a piece of tin-foil. When the 
shellac has dried, cut the foil in diamond-shaped or 
square sections with a sharp knife. Leave an edge 
§ inch wide at either side for contact to ground and 



52 



BOYS' BOOK OF ELECTRICITY 



conductor of the machine. A spark crossing the 
pane will be broken up in many bright little flashes. 

On the same principle, a design glass with almost 
any simple picture can be prepared. For this a zig- 
zag strip of tin-foil -|-inch wide should connect the wider 
strips at each end. Where the strip is cut the sparks 
will jump, forming the design. 





Fig. 32. — Spark pane. 



Fig. S3- — Electric spark design. 



It is also- possible to produce a fairly steady light 
from an ordinary lamp bulb and a static machine. 
The bulb should be one that is "burned out." It 
should be held by the glass part so that the brass tip 
is near the conductor, and the machine should be 
turned rapidly. The result is a glow that seems to fill 
the whole bulb. This can be seen only in a dark 
room. 

Attraction and repulsion is the principle of the 
jumping dice experiment. For this a small glass 
cylinder with a metal top and bottom is necessary. 



STATIC ELECTRICITY 



53 



Put a number of cubes of pith in the cylinder and 
connect the upper plate with the conductor of the 
static machine. When electricity is generated the 
cubes jump as if they were being shaken. This is 
due to the fact that they are first attracted to the 
top plate and then repelled from it. By setting the 
two plates vertically and insulating the one con- 
nected to the conductor, paper butterflies hung by 
silk threads will flutter back and forth between the 
plates. 

fo Conductor 




To Ground 
Fig. 34. — Shaking dice. 



The mechanical force of a static discharge is illus- 
trated by a mixture of sulphur and red lead shaken 
from a muslin bag on a charged piece of glass. The 
dust is electrified when shaken. Sulphur becomes 
positive and red lead negative, the two powders 
combining in symmetrical figures. The glass can be 
electrified with a point leading to an electric machine 
or by the spark from a Leyden jar. The figures that 
result are called Lichtenburg figures after their dis- 
coverer. 



54 BOYS' BOOK OF ELECTRICITY 

LIGHTNING 

Heavy lightning discharges are caused in much the 
same way as those from a Leyden jar. There is no 
more mystery than in the experiments you can per- 
form. The blinding flash and the thunder are merely 
enlargements of the crackling spark drawn from the 
cylinder machine. 

The immense area of the clouds and the distance to 
the earth allow an almost unlimited voltage to mount 
up before the flash breaks across. It is estimated 
that a stroke of lightning has an average value of 
50,000 volts per foot of length. An average figure for 
the actual energy spent is 250,000,000 horsepower. 
This enormous amount is used in an instant. The 
figure given by one authority is 100 5 000 of a second. 

One of the first intelligent ideas of lightning was 
that it is really caused by friction of the clouds. The 
later theory depends on the condensation of mist into 
raindrops. According to this, lightning is caused by 
rain. Each drop of mist is at first lightly charged by 
friction. Suppose we imagine that each particle has 
one charge. This is on the surface — not inside the 
drop. Striking together, a hundred of these might 
form one raindrop. There would be a hundred times 
as much water in a big drop as in each little particle, 
and also a hundred charges. There is not near as 
much as a hundred times the amount of surface to the 
big drop as to all the little ones. All the charge must 



STATIC ELECTRICITY 



55 



crowd into a space only about ten times as great as all 
the original drops had. As the drops strike together 
and become larger the static voltage runs very high. 
The positively charged cloud produces an equal nega- 
tive charge by induction on the ground, water, trees, 



Positively Chatged Ctauit 




*;V ♦"* * 



x 




Fig- 3S> — Field of static electricity around an unrodded house. 



and whatever makes up the other plate of this natural 
Leyden jar. The spark jumps across the hundreds of 
feet that separate clouds and earth. 

One of Franklin's most important discoveries about 
lightning was that the static discharge from sharp 



56 



BOYS' BOOK OF ELECTRICITY 



points equalized the charge gradually. The electrical 
condition of a lightning-rodded house, one without 
rods, and the readjustment when the spark occurs are 
shown in Figs. 35, 36, 37. 

There are certain objects which do not seem to need 
protection and which seem to be free from all lightning 








Ground Connections' 
Fig. 36. — Field of static charge around a well-rodded house. 



danger. Among these are: trains and locomotives, 
buildings with metal sides of frames, well-grounded 
steel windmill towers, steel battleships, and city busi- 
ness blocks. All of these objects allow so much 
leakage that the charges escape as fast as they form, 



STATIC ELECTRICITY 



57 



and the voltage never reaches a high enough value to 
produce a flash of lightning. 

Where lightning-rods are used great care should 
be taken to see that they are well grounded. If the 





Fig. 37. — Charge equalized by lightning flash. 

ground is imperfect the rod is worse than none at all. 
A good lightning-rod not only helps to prevent the 
lightning from striking, but conducts it to the ground 
without damage to the house when the charge is 
produced too suddenly to be prevented. 



58 



BOYS' BOOK OF ELECTRICITY 




STATIC ELECTRICITY 



59 



LIGHTNING-ROD EXPERIMENTS 

The Thunder House. — This toy house shows the bad 
effects of a poorly grounded rod. The house can be 
built easily of boards from a cigar box, and put to- 
gether as shown with small hinges. These shouid 
work easily. The lightning-rod should be tipped 
with a ball, and should reach to within \ inch from 
the tin-foil ground. The house is held together by 



Broom Straw 



To outer 
Coating 
o/JarO 




Rubber Band 



Fig. 39. — Thunder house. 



a broom straw or splinter of wood, bridging the gap 
between rod and ground. This straw extending 
through a little ring holds the entire house together. 

Bring a charged Leyden jar near the ball at the tip 
of the rod and a spark jumps across, flashes down 
the rod, and by breaking the straw releases the catch. 
The house falls apart of its own weight. 

The lightning ship is an experiment very similar. 



60 BOYS' BOOK OF ELECTRICITY 

In this the straw holds the mast of a little boat. 
When the ship is struck the mast falls over on the 
deck. A large tin dish can be used to contain the 
water, and a metal plate suspended by silk threads 



To Disc harg er 




To 
Tin/oil Coating 

Fig. 40. — A shipwreck. 

makes a good cloud. As the ship passes under this 
cloud, which is connected to a charged Leyden jar, 
the spark jumps to the tip of the mast, and causes a 
shipwreck. 



CHAPTER III 

Electric Batteries and Galvanic Electricity 

The electric battery changes chemical energy into 
electricity. It is a common saying that electricity is 
generated, but this is not strictly true. We cannot 
make electricity any more than we could create wood 
or iron. We can only direct its production. 

Electricity, light, heat, and chemical change are all 
forms of energy. They are interchangeable. Light 
is changed to heat when the sun's rays strike the earth; 
heat changes to light in a red-hot iron; electricity 
changes to heat in a flat-iron, and to light in a lamp; 
heat is changed to electricity at the generating station. 
In the battery a piece of zinc is consumed slowly, in 
much the same way as coal is burned under the boilers 
at the power-house. 

Electricity from a battery is quite different from the 
static electricity of the electrophorus and cylinder 
machine. It flows as a steady current, will spark only 
ashort distance, and is conducted only by metals and 
solutions of metal salts. In spite of the great differ- 
ence in form, a static machine caused the discovery 
which led to the perfection of the chemical battery. 

An Italian physician whose wife was sick, so the 
story goes, brought her a few frogs' legs for soup. 

61 



62 BOYS' BOOK OF ELECTRICITY 

One of these legs was laying on a table near a large 
static machine which he used for treating patients. 
The woman accidentally gave the crank of the machine 
a turn. At the same moment she happened to touch 
the leg with a knife. There was a sudden twitch of 
the muscles; the frog's leg moved. When she told the 
doctor he was interested and determined to find the 
cause. After many experiments he discovered that 
the same twitching could be produced without the 
static machine if he touched one end of the frog's 
leg with a piece of zinc and the other with a piece of 
copper, and then touched the free ends of the metals 
together. This was the very first electric battery. 
The physician was Galvani, and from his name came 
the terms "Galvanic battery" and "Galvanic elec- 
tricity," although he called it animal electricity and 
believed it came from the muscles and nerves of the 
frog's legs. 

The theory of animal electricity did not satisfy 
every one. Volta believed that the metals played a 
very important part. To prove this he built up a 
pile of zinc and copper plates, with flannel soaked in 
acid between each pair. It produced small currents, 
and proved that he was right. This arrangement of 
plates is called a "Voltaic pile," after the inventor, 
from whose name the word "Volt" is also taken. 

A simple electric cell is made up of two metals, and 
a solution which acts upon one of the metals. The 



BATTERIES, GALVANIC ELECTRICITY 63 



other metal is not affected and may be replaced by 
carbon. These two metals, or metal and carbon, are 
called the electrodes. Carbon and zinc are the most 
commonly used. The zinc is the positive electrode, 
or anode, and the carbon the negative, or cathode. 
Both of these words are from the Greek. The solu- 
tion of the cell is called the electrolyte. One pair of 
electrodes and their electrolyte should be spoken of 
as a cell, and not as a battery. The term "battery" 
indicates a number of cells all connected together. 

A cell having all the necessary ele- 
ments may be made in a few minutes 
from a plate of zinc and one of copper 
immersed in a glass of dilute sul- 
phuric acid. Place the lower ends of 
the strips as far apart as possible and 
let the tops lean together. Each of 
the elements of the cell is now in con- 
tact with two others. Copper is touch- 
ing zinc and acid, zinc is touching 
copper and acid, and the acid immerses the lower part 
of both metals. The same effect is secured if the 
electrodes are straightened up and connected by a 
wire. Current flows from the zinc through the acid 
to the copper and back along the wire. As the cur- 
rent outside the cell flows from copper to zinc the 
terminal on the copper is called the positive terminal 
and that on the zinc the negative terminal. This 




Fig. 41. — A simple 
zinc-copper cell. 



64 



BOYS' BOOK OF ELECTRICITY 



current is too weak to make a spark, but can be felt 
by touching both wires to the end of the tongue. 
This slight excitation affects the delicate nerves and 
produces a noticeably salty taste. 

The force by which current is sent through the 
wires is called the electromotive force and is abbre- 
viated into E. M. F. Other common terms for this 
force are "voltage' ' and "potential." 





Fig. 42. — Cell when current is not 
flowing. 



Fig. 43. — Cell when current is flow- 
ing. 



When the electrodes are put into the zinc-copper 
cell described you will notice that small bubbles rise 
from the zinc. Leave the cell connected for several 
days, and the zinc will be entirely eaten away, while 
the copper is not affected at all. This bubbling and 
corrosion are the only way in which you can see the 
change that is being made from chemical energy to 
electrical energy. 



BATTERIES, GALVANIC ELECTRICITY 65 

All the time the cell is working the zinc is being 
consumed and hydrogen gas is forming in little 
bubbles at the copper electrode. This hydrogen 
which comes from the solution is a great hindrance 
to the proper working of the cell. It surrounds the 
electrode and protects it from the solution. This 
action is called "polarization." To prevent it a 
material known as a "depolarizer" is used. Any 
substance that absorbs free hydrogen easily is a de- 
polarizer, and will keep the cell at its normal strength, 
even when the circuit is closed for some time. 

In an ordinary zinc-copper cell with acid solution 
the zinc would be eaten away nearly as soon with 
the circuit open as with it closed. This chemical 
change takes place only because of the impurities in 
the metal. It is known as "local action." As this is 
very wasteful and not at all necessary, it is avoided in 
nearly all zinc cells by coating the metal with mercury 
amalgam. This prevents the waste in a great 
measure. To apply the amalgam the zinc must be 
cleaned with acid and then rubbed with pure mercury 
until it takes on a silvery appearance. 

FORMS OF CELLS 

On account of polarization it is useless to make 

an ordinary zinc-copper cell, using acid electrolyte, 

with the hope of getting enough current to run a 

motor or operate induction or spark coils for any 

s 



66 



BOYS' BOOK OF ELECTRICITY 



length of time. With a carbon electrode instead of 
the copper, a better result can be secured, and this 
arrangement is used in a cell known as the "carbon 
cylinder" type. The carbon electrode is in the form 
of a cylinder, in the middle of which the zinc is sus- 
pended. An electrolyte made up of sal ammoniac 
and water is used. 

A still further improvement can be made by pro- 
viding a depolarizer to combine with the free hydrogen. 





Fig. 44. — Carbon cylinder cell. 



Fig. 45. — Leclanche cell. 



Manganese dioxide held in a porous cup around the 
carbon electrode produces the desired effect. With 
this addition the cell will deliver current and keep its 
voltage for a much longer time than before. This 
depolarized cell with sal ammoniac electrolyte is 
known as the Leclanche cell. 

The Daniell cell, and the gravity cell which is a 
variation of the Daniell type, are the most popular 
for uses that require steady current. In one form the 



BATTERIES, GALVANIC ELECTRICITY 67 



outside container is a copper cylinder. This forms the 
negative electrode. The positive or zinc electrode is 
inserted in a cup of unglazed porcelain. This con- 
tainer allows the current to pass, while the liquid inside 
the cup and outside of it cannot mix. 

To set this cell at 
work the copper con- 
tainer is filled with cop- 
per sulphate solution. 
Copper sulphate is "blue 
vitriol," or "bluestone." 





Fig. 46. — Gravity cell. 



Fig. 47. — Zinc "crow's foot" of grav 
ity cell. 



Plenty of this must be supplied to keep the solution 
saturated. A handful of crystals are generally left 
right in the solution. 

In the porous cup a solution of 1 part sulphuric 
acid to 20 parts of water is poured. 

Polarization cannot take place in such a cell be- 
cause the hydrogen that comes from the zinc is seized 



68 BOYS' BOOK OF ELECTRICITY 

and held just as it leaves the porous cup. Copper 
from the solution takes its place and is deposited on 
the copper container. 

In the gravity cell the electrodes are the same, but 
no porous container is used. Both electrodes are 
contained in a glass jar. The zinc is at the top in the 
shape called a crow's foot, and the copper at the 
bottom. A saturated solution of copper 
sulphate with a little sulphuric acid added 
is poured around the copper electrode, and 
on top of this a weak zinc sulphate solution 
is added. When in action the zinc sul- 
phate surrounds the zinc electrode at the 
top, while the copper sulphate remains at 
Fi f; 4 f;~ the bottom of the cell. This cell has to be 

Dry cell. 

kept at work. If the circuit is opened for 
any length of time the liquids mix and the strength 
of the cell is lost. 

The dry batteries which are ordinarily used for 
bell ringing, automobile engine ignition, and so on, 
are a form of the Leclanche cell. These convenient 
cells have not enough moisture to spill, and in that 
sense are dry, but they depend on an electrolyte for 
their action. There must always be enough moisture 
inside to make the chemical change. One common 
form of "dry" cell is shown in the sectional view 
(Fig. 49). The "mix" which surrounds the carbon 
electrode is made of manganese dioxide, ground coke, 




BATTERIES, GALVANIC ELECTRICITY 69 

and graphite. The electrolyte, which is sal ammo- 
niac, is contained in this mix and also in the pulp- 



-Donel Cap 




rXnur/ Wur- 

Acorn Mead Post 

Sea/ 

Sand 

Sa wdusr 

Putpboard L mmg 



Car don E/ecrrode 



Z>nc Con 



Pulpooord Bottom] 



Fig. 49. — Inside of dry cell. 



board lining of the cell. Zinc chloride is sometimes 
added to reduce local action and lengthen the life of 
the cell. 

MAKING CELLS 

There is no economy in making batteries; a good 
cell can be bought for about the price of the raw 
materials. In spite of this it is a good thing to build 
some cells, as in doing the work yourself you secure a 
better idea of the action and construction than any- 
one could possibly give you. The chemicals needed 
are common and can be had at any drug store. Old 
dry cells will supply both zinc, carbons, and con- 
nectors. 



7° 



BOYS' BOOK OF ELECTRICITY 



A Leclanche cell may be made easily by using a 
glazed milk crock for the outside container and a 
porous flower-pot for the inner. These materials are 
selected because they can be secured anywhere. The 
flower-pot chosen should be new and clean and of 
sufficient height to stand a little above the edge of 
the crock. While the illustrations show a crock 
with sloping sides, the straight-sided kind is even 
more desirable. 

The carbon and zinc electrodes needed for this cell 
can both be taken from an old dry battery. Cut 





Fig. 50. — Copper electrode for Daniell cell and zinc for Leclanche cell. 



down the side at the joint with a cold chisel and 
take off the bottom. Then trim off evenly so that 
the zinc left will stand a little shorter than the flower- 
pot. Clean the zinc thoroughly with hot washing 
soda. The plate is ready to be amalgamated. Both 
sides should be rubbed with mercury until they are 
silvery in appearance. An old tooth-brush is a good 
thing to use for rubbing on the amalgam. 

In preparing the flower-pot as a porous cup, first 
dip an inch of the top in a bath of melted paraffin, 



BATTERIES, GALVANIC ELECTRICITY 71 

letting it stay until it is well waxed. A plug of wood 
also soaked in paraffin should be used to stop up the 
hole in the bottom. Now spread a layer of manganese 
dioxide and powdered carbon, mixed in equal quanti- 
ties, in the bottom of the pot. Stand the carbon 
upright in the center. Pack in more of the carbon 
and manganese dioxide around it, and the porous 



Carbon 

Pa ra ffi n 



Zinc 




$al Ammoniac 

Manganese 
Dioxide 



LECLANCHE 



5ulphunc 
Acid 




Copp 

DANIELL 
Fig. 51. — Leclanche and Daniell type "milk crock" cells. 

cup is complete. When this is in place in the crock, 
and the sal ammoniac solution poured in and around 
it, the cell is ready for action. A well-paramned 
wood cover can be added to give a little more finished 
appearance. Four ounces of sal ammoniac is about 
the right quantity for this cell. When the solution 
becomes weak after use it will appear milky. More 



72 BOYS' BOOK OF ELECTRICITY 

sal ammoniac should then be added. The zinc will 
also need to be renewed. 

With exactly the same arrangement of electrodes 
a cell can be made with chloride of lime and common 
salt. The chloride of lime is packed around the 
carbon rod in place of the manganese dioxide and car- 
bon. A strong solution of common salt replaces the 
sal ammoniac solution. 

With a change in electrodes the milk crock and flower- 
pot can be used to make up a Daniell cell. In this the 
copper should be cut in a sheet long enough to make a 
cylinder that will go clear around the flower-pot. The 
zinc can be an amalgamated rod or a dry-cell casing. 
Two electrolytes are used. Dilute sulphuric acid 
should be poured around the zinc, and a copper sul- 
phate solution in the large crock. A bag of " bluestone" 
should be suspended over the edge of the crock or a 
shelf made of copper to hold the crystals. 

Another simple form of cell can be made from an 
empty tomato can. This should be provided with a 
porous earthenware container of about the same 
height, but 2 inches smaller. If a porous jar is not 
available a container can be made from blotting-paper. 
With the help of pasteboard made in the form of two 
cylinders a very good plaster-of-Paris container may 
be made for this or the other fluid cells. The plaster 
should be thoroughly dried by standing it in the sun 
for several days, or baking it a few hours before use. 



BATTERIES, GALVANIC ELECTRICITY 73 

Iron filings and turnings packed in the bottom of 
the can and around the porous cup make up the nega- 
tive electrode. As borings and turnings from a ma- 
chine shop are usually greasy, they should be boiled 
for a few minutes in a strong solution of washing soda 
and rinsed in clear water before use. The positive 
electrode is a piece of zinc suspended inside the cylinder. 



Wood 
Coyer 




Fig. 52 — Tin-can cell. 



Fig. 53. — Pasteboard cylinders 
held in place by hatpins for casting 
porous containers. 



To prepare for use, a solution of caustic potash is 
poured over the turnings and around the porous cup. 



MAKING A DRY CELL 

The dry cell is called "dry" only because there is 
not enough liquid in it to spill. It is really a form of 
Leclanche cell as generally made. The electrolyte 
is a sal ammoniac solution. It is held in the porous 
lining and in the depolarizer. 



74 BOYS' BOOK OF ELECTRICITY 

To build a dry cell you will first need a zinc can 
about the size of a standard dry-cell container. Solder 
the edges carefully and be sure the joints are all right. 
Cut a lining of blotting-paper to fit closely in the bot- 
tom and at the sides, reaching nearly to the top. 
Secure a carbon from an old cell. The connector 
should be in good condition for use. 

Make up this mixture for the electrolyte and depo- 
larizer: 

Manganese dioxide ioo parts. 

Graphite 20 parts. 

Sal ammoniac 20 parts. 

Zinc chloride 20 parts. 

Add enough water to make the mixture into a thick 
paste. Put a J-inch layer of this in the bottom of 
the can, pack it firmly, and place the carbon upright in 
the center. Then fill in the rest of the electrolyte to 
within ^ inch of the top of the can. Pour a mixture of 
beeswax and resin over the top, leaving a small vent 
for the escape of gas. 

SINGLE-FLUID CELLS 

All the cells described have been double-fluid cells. 
In other words, the depolarizer was held in a porous cup 
with the negative electrode. In the single-fluid cell 
it is dissolved in the electrolyte. The single-fluid cell 
is easy to build, but needs a good deal of care. The 
chromic acid compound sold as depolarizer or "electro- 



BATTERIES, GALVANIC ELECTRICITY 75 

poian" fluid eats the zinc very rapidly. When the 
cell is not in use the positive or zinc electrode must be 
lifted from the solution and washed. 

Either zinc and carbon or zinc and copper electrodes 
may be used with the single-fluid cell. A large fruit 
jar or straight-sided crock makes a very good container. 
No cover is needed. If two flat zinc and copper plates 



'0^X1 




Zin$ 



Copper 





Carbon 



Carbt 



Fig. 54. — Mounting plate metal elec- 
trodes. 



^ ^^Zinc 



Fig. SS« — Mounting for carbons and 
zinc rod. 



are used they may be screwed to each side of a wood 
strip long enough to extend over the sides of the jar. 
This strip should be well boiled in paraffin. Care 
should be taken that the screws holding one plate do 
not touch the screws in the opposite one. Each plate 
should extend a little above the strip to leave room for 
binding-screws. Carbon can, of course, be used in 
place of copper. Carbons taken from old dry cells 



7 6 



BOYS' BOOK OF ELECTRICITY 



answer very well, but great care must be taken in 
boring the screw holes, as the strips are hard and quite 
brittle. 

Where round electrodes instead of plates are used, 
a better support can be built by arranging two small 
square sticks as clamps and screwing them together 
with the electrodes between. Each stick should be 





Fig. 56. — Complete fruit jar cell. 



Fig. 57. — Mounting for four carbons 
and one zinc electrode. 



notched to receive a zinc rod in the middle and a car- 
bon rod on each side. The strips should be long 
enough to extend over the sides of the crock, and 
should be well soaked in melted paraffin. A long 
screw through each end of the sticks holds all three 
electrodes in place. 
A very good arrangement of electrodes which gives 



BATTERIES, GALVANIC ELECTRICITY 77 

a large surface of carbon is secured by screwing four 
carbons to a square piece of wood and putting down a 
rod of zinc in the center. All the carbons should be 
connected together by a piece of wire. 

To get good results with any of these pairs of elec- 
trodes the special depolarizing solution should be 
used. A very good one is: 

Chromic acid 20 parts. 

Water 80 parts. 

Sulphuric acid 10 parts. 

Chlorate of potash 1 part. 

Remember that this solution consumes the zinc very 
rapidly. The electrodes should always be taken out 
and washed when the cell is not in use. 

HANDLING CHEMICALS 

The workroom is the only place for handling chem- 
icals. Sulphuric acid will quickly ruin rugs or carpets if 
allowed to spatter on them. Other necessary chemicals 
will leave a bad burn on the skin if not washed off 
quickly. Sulphuric acid is neutralized by ammonia. 
A bottle of strong ammonia solution should be kept 
close at hand when working with acids. A few drops 
of it put on a cloth burned by sulphuric acid will 
sometimes bring back the color and save the cloth. 
Caustic potash gives at first a soapy feeling to the 
fingers, but quickly eats through the flesh and leaves a 
very bad burn. It should never be touched with the 



78 BOYS' BOOK OF ELECTRICITY 

fingers. In case it is accidentally touched, wash the 
spot quickly with a weak acid solution, and then hold 
the hand in a stream of running water. 

Neither of these remedies take the place of careful 
handling of chemicals. Always wear old clothes 
when working with batteries. In addition, try not to 
spill or spatter the acids or caustic solutions. Unless 
proper precautions are taken it is better not to experi- 
ment with cell making at all. 

A point always to be remembered in mixing acid 
and water is to add the acid to the water, and not the 
water to the acid. Acid should always be poured in 
slowly and the mixture stirred gently. 

BATTERY CONNECTIONS 

The E. M. F. or voltage of each one of the batteries 
described has an unchanging value. In the Daniell 
cell the E. M. F. is 1.08 volts; in the Leclanche, 1.48 
volts; in the tin-pot cell, 1.14 volts, and so on. If these 
were made as small as a thimble or as big as a wash-tub 
the voltage would not change. The big ones would 
only deliver more current. 

Either voltage or current may be increased by con- 
necting a number of cells together. For increasing 
the E. M. F. the connection must be in series. The 
series connection consists in wiring the carbon of each 
cell to the zinc of the next. The E. M. F.'s are thus 
added. With the parallel connection the E. M. F. is 



BATTERIES, GALVANIC ELECTRICITY 79 

not increased, but the cells will deliver a much heavier 
current. Either of these arrangements is called a 
battery. 




Parallel Connection 




Series- Parallel Connection. 
Fig. 58. — Connections for dry cells. 



STORAGE CELLS 

Where a considerable battery current is wanted for 
some time, even the Daniell cell is not entirely satis- 
factory. For running electric automobiles, electric 
launches; for electric lighting and starting of automo- 
biles the storage battery or secondary battery is used. 

"Secondary battery" is a more correct name than 
"storage battery," for although electricity seems to 



8o 



BOYS' BOOK OF ELECTRICITY 



be stored in the jars, it is not. The current used to 
charge the cells really forces a chemical change in the 
metal electrodes. Changing back to their original 
form, they generate an E. M. F., and will deliver cur- 
rent until the change is complete. The chemical 
change takes place only when the electric current is 
being used. Using current from the cell is spoken of 
as "discharging" the cell. 




Fig. 59. — Storage battery. 

As in the primary cell, the active parts here are a 
negative plate, a positive plate, and an electrolyte. 
The plates are called grids because of their peculiar 
shape. 

Instead of using two metals, both grids of the second- 
ary cell are usually made of lead. This is cast quite 
thick, and is filled on both sides with little pockets to 
contain the active material. The latter is really re- 
sponsible for the work of the cell, and the lead plates 
only act as supports and conductors. 



BATTERIES, GALVANIC ELECTRICITY 81 

In the most common form of secondary cell the active 
material of the positive plate or anode is lead peroxide. 
At the negative plate the material is a spongy form 
of metallic lead. Sulphuric acid is the electrolyte. 

Other metals and other electrolytes can be used to 
good advantage in building storage cells. In the 
Edison cell the metals are nickel and iron, with a 
caustic potash electrolyte. This cell is very light 
and strong. 

HOW TO MAKE A STORAGE CELL 

Secure enough sheet lead \ of an inch thick for three 
plates of a size to fit any square glass or glazed crockery 
jar available. These should be rectangular, with a lug 
at one corner, and all the same size. Roughen two of 
them on one side with a sharp chisel, always cutting 
downward. Roughen the third in the same way on 
both sides. When through the plates should be full 
of little points all turned upward. 

On a piece of clean glass mix a paste of red lead and 
sulphuric acid. The acid should be diluted with an 
equal quantity of water. Use a flat paddle to make 
the mixture uniform. Coat all the plates thinly on one 
side with this, taking care to press it into the little dents. 

Let the paste harden for a few hours. Coat the 
roughened side of the third plate. Now cut thin 
pieces of wood of the same width as the plates, but a 
little longer. These are called separators. One should 



82 



BOYS' BOOK OF ELECTRICITY 



be placed on each side of the plate to go in the middle, 
and the three plates laid together. The coated sides 
of the outer plates should rest against the separators. 
To set up the cell, bolt the two outer plates together, 
passing the bolt through the hole in the projecting 
lugs. To keep the plates a proper distance apart lead 
washers cut from sheet lead should be used. After 



O 




Fig. 60. — Lead sheet for battery Fig. 61. — Plate prepared for red 
plate. lead paste. 

the bolt is drawn up and the wood separators are in 
place between the plates, stout rubber bands should 
be put around all three plates at top and bottom. 

The electrolyte used should be made up of 5 parts 
of water to 1 of sulphuric acid. The acid should be 
poured slowly into the water. On account of the heat 
that is generated by the combination the mixture 
should be stirred constantly with a carbon rod. A 



BATTERIES, GALVANIC ELECTRICITY 83 

glazed earthenware jar is a better container for mixing 
than a glass jar. Acid of proper strength for a storage 
battery has a specific gravity 1.2 times as great as 
water. Battery men call this "1200 acid. ,, If there is 
a garage handy where electric automobile batteries 
are charged, 1200 acid can be bought already mixed. 

Place the plates in the jar, and add enough acid to 
cover the coating of active material. They are now 



p To Zinc 




- To Copper 




Fig. 62. — Lead plates completed, 
with separators between. 



Fig. 63. — Storage cell assembled. 



ready for the first, or forming charge. The middle 
or positive plate should be connected to the positive 
(copper) pole of a primary battery. One of the out- 
side plates should be connected to the negative zinc 
pole. The battery supplying the current should be 
made up of three Daniell or chromic-acid cells con- 
nected in series. Current should be allowed to flow 



84 BOYS' BOOK OF ELECTRICITY 

for a couple of days. After the first charge much less 
time is needed. 

CHOOSING THE RIGHT CELL 

Each cell has features that make it especially desir- 
able for certain kinds of work. Some have a much 
higher E. M. F. and longer life than others. Some 
will work well only when current is flowing most of the 
time, and others must be allowed to rest after being 
used. The first class is known as the closed-circuit 
cell, and the second as the open-circuit cell. 

The " tin-pot' ' cell, the dry batteries, and the 
Leclanche cell are all well suited for bell ringing, tele- 
phone work, and other service where current is only 
needed a small part of the time. 

The commercial dry battery as made today is so 
well depolarized and has such remarkable recuperation 
that the short period of rest between sparks in an auto- 
mobile engine are as much as it needs to get rid of the 
free hydrogen. 

When the circuit is really to be closed for weeks at a 
time, the best cell is the Daniell, of the gravity type. 
This is used in telegraph work. It is an excellent cell 
to use for the chicken thief or burglar alarms. The 
gravity cell must be kept at work all the time or it will 
soon get out of order. A long piece of insulated wire 
coiled up and connected between the two poles answers 
the purpose very well. This keeps up the chemical 



BATTERIES, GALVANIC ELECTRICITY 85 

action by allowing a small current to flow, and keeps 
the zinc sulphate at the top and the copper sulphate 
at the bottom, where they belong. 

Where heavier currents are needed the storage cell 
is better than a primary cell. Care should be taken, 
however, not to use too great a current, or the active 
material drops off the plates and will quickly ruin the 
cell. 



CHAPTER IV 

Electric Circuits 

When the zinc and copper plates of the simple 
voltaic battery were allowed to come together, current 
flowed from the zinc to the copper, up the copper, 
down the zinc, and so on. Adding a piece of copper 
wire between the terminals made no difference except 
to lengthen the path. In either case the current fol- 
lowed a metal away from one electrode and back again 
to the other. This path is called an electric circuit. 
The circuit is closed when current is allowed to flow 
from one side of the cell or battery back to the other. 
When either side of the battery is disconnected the 
circuit is open. 

Current cannot flow unless the "circuit" is closed. 
The E. M. F. is generated whether the circuit is closed 
or open. 

Voltage and current can be compared to pressure 
and flow of water. Imagine two water barrels half- 
filled and connected at the bottom by a short piece of 
pipe. The pipe can be closed with a valve. If the 
two barrels are filled to the same level there is no flow 
from one to the other even if the valve is open. There 
is no "voltage" and no "current." Now suppose the 

86 



ELECTRIC CIRCUITS 



8? 




&& 



BOYS' BOOK OF ELECTRICITY 



valve is closed and all the water pumped from one 
barrel to the other. The full barrel exerts a pressure, 
but cannot force water into the other. The condition 
is similar to an open circuit. Opening the valve has 
the same effect as connecting the two poles of an elec- 
tric battery with a piece of wire. Water flows through 
the connecting pipe until the two levels are equal. 

If water is continually pumped from one barrel into 
the other and allowed to flow back through the pipe 



Water_ 
Level 




Water 
Level 



Fig. 65. — These water barrels can be compared to an electric circuit. 

at the bottom, we have a condition that can be likened 
to a complete electric circuit. We apply the E. M. F. 
by pumping. The " circuit " is from one barrel through 
the pump into the other barrel and back through the 
pipe. 

All the principles of the electric circuit are the same 
for batteries as for electric railroads, great power sys- 
tems, and long transmission lines. Current must al- 
ways go out from the power plant, do its work, and 
come back. The current is not used, but simply 



ELECTRIC CIRCUITS 89 

forced around the circuit by the electromotive force, 
or E. M. F. 

In transmission lines the circuit is all carried under- 
ground or out of reach on poles or towers. In a rail- 
way system it goes out on the trolley wire, comes 
down through the metal circuit in the car, turns the 
motor, and returns to the power-house. The E. M. F. 
is supplied by steam or water power, but the result 




Fig. 66. — Voltmeter for testing batteries. 

would be just the same if large batteries of storage cells 
were used. 

E. M. F. is measured in Volts, just as water pressure 
is measured in pounds. In the primary cell the E. M. 
F. is always somewhat less than 2 volts, and in some 
it is under 1 volt. Incandescent electric lights are 
commonly used at pressures of no, 125, or 250 volts. 
Street car lines use 550 volts in the city, and often 
much higher on suburban lines. In long electric trans- 
mission lines the voltages in use are as high as 50,000 



go BOYS' BOOK OF ELECTRICITY 

volts, and sometimes even more than 100,000. Any 
E. M. F. higher than 125 volts should be considered as 
dangerous. 

Current is measured in Amperes. When an ordinary 
incandescent lamp is turned on a current of about 
\ ampere is flowing. This current leaves the station 
flowing at a speed of more than 186,000 miles per 
second; the same velocity as a ray of light. Flash- 
ing to the furthest ends of the system, it enters homes 
to be turned to light in the delicate filaments of the 
electric lamp, or to heat in the flat-iron. This current 
all goes back to the station. In big stations the flow of 
current is often enormous. If a lamp could be made 
large enough to take all the current supplied by a single 
one of the machines at Fisk Street Station in Chicago 
it would shine with a brilliancy of about 30,000,000 
candlepower. The copper conductors that take cur- 
rent to and from two of the Chicago stations contain 
nearly 70 tons of metal. If drawn out into wire -^ 
inch in diameter, this would be more than enough to 
build a telephone line from Chicago to Panama. 

As mentioned before, current has to be forced to 
flow, even over a copper wire. Something about the 
wire actually opposes the flow of current. This opposi- 
tion is called "resistance." The harder the current 
is to force along the substance, the greater its resistance 
is said to be. 

Substances with low electrical resistance are called 



ELECTRIC CIRCUITS 91 



r 



conductors. Carbon, all metals, and salt solutions are 
conductors. 

Substances with very high electrical resistance are 
called insulators. Air, glass, hard rubber, and fiber are 
all good insulators. Current can be made to flow along 
even the best insulator, but the E. M. F. must be very 
high to move even a small current. 

A wire carrying current is " insulated " when it is 
separated from the earth or other conductors by insulat- 
ing substances. Telegraph, telephone, and electric 
light wires are insulated by their glass or porcelain 
supporting knobs, and sometimes by a rubber covering. 
Where the E. M. F. is very high a type of insulator 
known as the "petticoat" insulator is used. The 
petticoats act as little umbrellas to keep the under 
side of the insulator dry. 

When two sides of a circuit are allowed to come to- 
gether with no resistance between, the line is short 
circuited. If one side of the circuit touches the ground 
the line is said to be grounded. 

The size and length of the wire determines its resist- 
ance. Just as water flows easier through a large short 
pipe than a small long one, so current flows easier 
through the short thick wire. 

Resistance is measured in Ohms. The Ohm, Ampere, 
and Volt were all named after scientists. As electrical 
units they are very closely united to each other. The 
relation is simple. An E. M. F. of one volt is required 



92 BOYS' BOOK OF ELECTRICITY 

to force a current of one ampere through a resistance of 
one ohm. Putting this in another form, the resistance 
of a circuit multiplied by the current flowing always 
equals the voltage. This can be expressed: 

E = CR 

E represents the E. M. F. or voltage, C is the current, 
and R is the resistance. This is called Ohm's law. It 
is generally written: 

which means that the current is equal to the E. M. F. 
of the circuit divided by the resistance. 

If, for instance, a current of 5 amperes flowed in a 
circuit, with an E. M. F. of 10 volts, the resistance of 
the circuit would be 

R = — or Resistance = — = 2 ohms. 
C 5 

The Watt is the unit of work. It is named in honor 
of the celebrated James Watt, who fixed the " horse- 
power' ' unit at the amount of power needed to lift 
33,000 pounds at the rate of a foot a minute. The 
number of watts changed to work or heat in any cir- 
cuit is the E. M. F. in volts times the current in amperes. 
Thus the power expended in an incandescent lamp 
might be no volts X J ampere, or 55 watts. Lamps 
are now generally spoken of in terms of watts, and are 



ELECTRIC CIRCUITS 



93 



commonly made in 25-, 50-, 60-, 100- watt, and many 
other sizes. 

In speaking of larger quantities of power the word 
" Kilowatt' ' is used. A kilowatt is 1000 watts. It is 
equal to about ij horsepower. Electric power is 
bought and sold not by kilowatts, but by kilowatt 
hours. A kilowatt hour might be a kilowatt used for 
an hour, or one watt used for a thousand hours, or 



^f¥W¥^ 



Incandescent Lamps 
tn Parallel 



%- 4r %■ 

Arc Lamps 
in Series 
Fig. 67. — Series and parallel lighting circuits. 



200 watts used for five hours. Average power multi- 
plied by time in hours gives kilowatt hours. It is 
abbreviated "kw. hrs." In some of the larger stations 
power is sold for as low as 2 cents per kw. hr. Or- 
dinarily the price is from 10 to 15 cents for electric 
light users. 

Circuits from a generating plant may be either in 
parallel or series, much the same as the batteries were 
connected. Incandescent lamps are usually wired in 



94 BOYS' BOOK OF ELECTRICITY 

parallel. With this arrangement the current goes out 
over one wire, then divides, part of it going through 
each lamp and returning on the other wire. The 
voltage is practically the same whether one lamp or 
many are used, but the current increases with the addi- 
tion of each lamp.' 

The series connection is used for some types of arc 
and incandescent lamps. With this arrangement all 
of the current has to pass through every lamp. A high 
E. M. F. is needed to force current through the com- 
bined resistance. As lamps are added the current does 
not increase, but the voltage does. For this reason the 
voltage of a line supplying current to series lamps is 
quite high, making the line somewhat dangerous. 



CHAPTER V 

Electromagnets 

When current flows in a circuit the wire is heated, 
and there is another even more important effect. The 
flow of current actually turns the wire into a temporary 
magnet. The material of the wire has nothing to do 
with the magnetic effect except to conduct the cur- 




s~$$0p*r/ 



Fig. 68. — Current in a wire attracts iron filings. 

rent. The magnetism can be shown quite plainly 
with two or three good primary cells connected in 
multiple. Run a piece of wire from a negative to the 
positive side through a little pile of iron filings. Lift 
the wire up and quite a bunch of filings will stick. 
Disconnect either end from the battery and they all 

95 



9 6 



BOYS' BOOK OF ELECTRICITY 



fall off. There is not a trace of magnetism left in the 
wire. 

The same effect is shown by a single cell and an ordi- 
nary pocket compass. Pass the wire over the top of 




Fig. 69. — Current directs a magnet needle. 

the compass parallel to the needle, and you will im- 
mediately notice a little vibration. When the deli- 
cately balanced needle comes to rest it will not be paral- 
lel to the wire, but pointing at an angle. Wind half 
a dozen turns of wire around the compass box, and 



Fine Insulated Wire 




Fig. 70. — Small currents can be detected with a compass fixed this way. 

the deflection will be still greater. By placing the 
compass on a neat board base, and winding the wire 
on it carefully, an instrument can be made that will 
detect very weak currents. 
These and many other experiments were first tried 



ELECTROMAGNETS 



97 



by Oersted in 1819. The facts discovered laid the 
way for the dynamo, motor, and much of the other 
electrical machinery and apparatus in use today. 

Oersted discovered that the magnetic field set up by 
an electric current is in every way like the field around 
a magnet. The lines of force even arrange themselves 
in the same way. Run a wire carrying current through 
a clean piece of cardboard on which iron filings have 
been dusted. Tap the card gently; the iron filings will 
group themselves in little circles around the wire. 




Fig. 71. — Lines of force around a wire carrying current. 

The lines of force they indicate surround every electric 
line carrying current, no matter how long it may be. 
As the field surrounds all the length of the wire many 
feet of it can be collected by simply winding the wire in 
a coil. It can be still further increased by putting a 
piece of soft iron inside the coil. Lines of magnetic 
force seem to find an easier path through iron, and 
crowd into it wherever possible. 

Without the iron core the coil of wire is called a sole- 
noid; with the core it becomes an electromagnet. 



98 BOYS' BOOK OF ELECTRICITY 

A glance at Fig. 72 will show how the lines of force 
wander outside the solenoid, and are collected by the 
iron core of the electromagnet. 

The north and south poles of solenoids and electro- 
magnets are determined by the direction of flow of the 
current. Remember that current flows from carbon 
electrode to zinc electrode in the circuit to which a 
battery is connected. A good way to remember polar- 
ity is to imagine a boy swimming with this current, 
facing toward the inside of the coil. In this position 



Fig. 72. — Coil without and with an iron core. 

his left hand would be toward the north pole and his 
right hand toward the south pole. 

A simple solenoid can be made by winding 50 or 75 
turns of fine wire around a small paper tube, and con- 
necting the two ends to the terminals of a primary cell. 
This will attract iron filings much better than a single 
wire, and will affect the compass needle quite strongly. 
If carefully balanced at the end of a long strand of silk 
thread, and connected by long wires to the cell, it swings 
to the north. 



ELECTROMAGNETS 



99 




Insert a nail part way in this tube and it will be drawn 
clear in. The solenoid has been made into an electro- 
magnet. It is considerably stronger than the bar mag- 



ioo BOYS' BOOK OF ELECTRICITY 

net, and behaves like it in every way but one. When 
the current stops, the magnetism disappears. 

If more turns are added and a piece of steel substi- 
tuted for the soft iron core, the steel will retain part of 
its magnetism for a long time. Very good permanent 
magnets may be made with the use of strong solenoids. 

Solenoids are used a great deal in electrical apparatus 
for opening and closing small switches; the circuit 
is opened or closed by a solenoid "core" which is 
drawn into the coil when current is flowing. They 
also are used to regulate the carbon of arc lamps. 

Electromagnets are by far the most widely used 
piece of electrical apparatus. Telegraph, telephones, 
motors, generators, and wireless all depend to a cer- 
tain extent on the action of the electromagnet. Mag- 
nets purely for attracting iron are made in a great many 
forms. Some with especially shaped poles have been 
built to take bits of steel from workmen's eyes. At 
the immense steel mills near Chicago iron is broker; 
up by lifting a big iron ball with a magnet, and then 
letting it drop by cutting off the current. These 
magnets, and magnets for carrying iron scrap or sheets, 
are made quite flat. This brings all the windings close 
to the poles, where the magnetism can be used to best 
advantage. 

ELECTRIC BELLS 

The electric bell furnishes a good example of an every- 
day use of the electromagnet. The circuit of a bell 



ELECTROMAGNETS 



IOI 



includes the coil, a contact which opens and closes the 
circuit, the batteries, and the push-button. All of these 
parts are wired in series; that is, when current flows 
it goes through every part. When you press the but- 
ton of an electric bell the circuit is closed through the 
magnet coil. The coils attract an armature of soft iron 
fastened to a spring. When the armature is attracted 



'4 



Bell 



u 



~?t\Push 
IP Button 



Dry 
dell 



Fig. 74. — Simple electric bell circuit. 



it is pulled away from the contact point. The circuit 
is opened and the coils are at once demagnetized. As 
there is no magnetic pull to hold the armature against 
the magnet, it flies back and the spring again touches 
the contact point. This completes the circuit once 
more. The armature is pulled by the magnet and the 
circuit again broken. Thus the hammer of the bell 



102 



BOYS' BOOK OF ELECTRICITY 



vibrates back and forth as long as the button is 
pressed. 

A good bell may be bought for about half a dollar. 
The experience gained in building a bell of your own 
make could not be bought at any price. In making a 
bell it is a good plan to lay out a base on a piece of J- 
inch wood to fit whatever gong you may have. If this 
is done before the wood is cut there is a chance to make 
changes as you go along. For the bell planned here a 




Fig- 75- — Magnet core for bell. 



2|-inch gong is used. If a gong of nearly that size is 
secured the dimensions laid down on the plan in Fig. 
80 can be followed. 

For the magnet core have a blacksmith bend a piece 
of J-inch iron rod into a U shape; when bent this 
should be 2 inches in length and f inch between the 
poles. This core should not be plunged into water, 
but should be allowed to cool slowly. When cool the 
whole surface should be filed smooth, and the ends filed 



ELECTROMAGNETS 



103 



or sawed off flat and true. At least \\ inch of each 
pole should be straight. The next step is to make two 
paper tubes that will just slide over the poles. These 
can be made by wrapping two or three turns of heavy 
paper around a stick whittled to the right size, and 



Fig. 76. — Spool for wire coil. 

gluing the turns together. Cut each tube if inch 
long, but leave them both on the stick. When the 
tubes have dried cut out two wooden ends for each. 
These can be made from cigar box wood planed to 




Fig. 77. — Windlass for winding wire on spools. 

about half-thickness. They should each be f inch in 
diameter, and should be carefully bored out so that they 
fit tight on the ends of the paper tubes. A little glue 
will hold them firmly in place. 
The two spools, or bobbins, can be left in place on 



io 4 BOYS' BOOK OF ELECTRICITY 

the stick for winding. At this point a little extra work 
will pay very well. Winding will be much easier if a 
small winding stand like the one shown in Fig. 77 is 
made. A piece of wire will do for the crank. 

For winding use No. 22 cotton-covered magnet wire. 
About 4 ounces will be needed. Before putting on the 



Z. 



>* 



Fig. 78. — Armature, spring, and tapper. 

first layer drill a small hole in the spool at the paper 
core and pull about 6 inches of wire through for con- 
nections. Wind evenly. A sheet of tissue-paper 
between layers will help in keeping the coils even. 
The last coils should be fastened by passing the wire 
under and pulling it tight. 




Fig. 79. — Block for holding magnet. 

The armature should be made of a piece of soft iron 
riveted to a clock spring. The wire on which the iron 
hammer is attached can be screwed in or riveted to the 
armature. In order to straighten the spring and bore 
the holes it must first be annealed. This is done by 
heating it to red heat and then letting it cool off very 



ELECTROMAGNETS 



105 



slowly in hot ashes or hot sand. After it has been 
drilled and bent to the proper shape it can be tempered 
by heating again and dropping in water. 

For mounting the magnet on the base make two wood 
strips exactly alike and each about 2 inches long, \ 




Fig. 80. — Inside of electric bell. 

inch wide, and \ inch thick. Chisel out a U-shaped 
groove in each one to receive the bend of the magnet. 
When screwed to the wood base these strips will hold 
the magnet firmly in place. 



106 BOYS' BOOK OF ELECTRICITY 

The spring can be tightly held by a small block of 
wood in which a fine saw cut has been made. For addi- 
tional tightening a small screw can be run through the 
block. See that the block is placed so that the soft 
iron armature is held about ^ inch away from the 
pole tips and parallel to them. In this position the 
end of the spring should just touch the contact screw. 

An ordinary brass screw held by a small block fas- 
tened to base serves very well as a contact. This 
screw can be turned until the bell works best. 




Fig. 81. — Common forms of binding-posts. 

All wiring connections are shown in Fig. 80. Current 
comes in through the coil to the spring and out through 
the brass screw. When the magnet pulls the armature 
the circuit is broken at the screw and the spring flies 
back, completing the circuit again. 

Binding-posts for the outside connections can be had 
in many shapes. For the bell, those with wood screws 
are convenient. Two are needed, and should be evenly 
spaced at the top of the board base. To one connector 



ELECTROMAGNETS 



107 



attach the fine wire running from the armature end of 
the magnet. Then connect the two wires left at the 
beginning of the coil. These should each be coiled 




Fig. 82.— Finished bell. 



tightly around a pencil to make a neat piece of work. 
The remaining wire should be run to the base of the 
spring, and fastened by a small screw. From the 
brass contact screw a piece of wire is connected to the 



108 BOYS' BOOK OF ELECTRICITY 

other binding-post. Connections to the binding-posts 
should be soldered, as this reduces the resistance of 
the joint. The connection at the contact screw should 
be left loose until the screw is regulated. It can then 
be soldered. 

A cover to protect the bell and give it a finished 
appearance should be made from cigar box wood. It 
should be just large enough to allow free working of the 
armature. A slot at the bottom will allow for move- 
ment of the hammer. Four small brass hooks and screw 
eyes can be added to hold the cover firmly in place. 

Finally, the base and box should be well smoothed 
with sandpaper and given two coats of shellac. 

WIRING THE BELL 

When the location of the bell has been decided, 
measure the circuit carefully, being sure to include the 
distance to the battery. No. 16 insulated wire is a 
convenient size to use for the circuit. It can be bought 
in any length needed. The best place to run this wir- 
ing to a door is through the basement. If this is 
not practicable, it should either be carried along the 
base board or over the picture molding. Fasten it in 
place with small insulated staples. Keep it out of 
sight as much as possible and make the turns square 
and neat. 

Especial care should be taken with wire joints, as 
one hastily made may introduce a high resistance and 



ELECTROMAGNETS 



109 



cause considerable trouble. Figure 83 shows the right 
and wrong way of making joints. The Western Union 
joint is both neat and easily made. While soldering 
is not absolutely necessary, it makes a much better 
joint. Either resin or one of the compounds sold for 
the purpose may be used as a flux. 

Push-buttons are so simple and cheap that it hardly 
pays to make one, though this is easily done. The 
only materials are a piece of brass spring, a brass 




Good Splice 

Fig. 83. — Wrong and right way of 
making splice. 



Fig. 84. — A push-button made from 
a pill box. 



screw, and a small wooden box. The screw serves 
both as a contact and a fastener for the bell. Cut a 
little slot through each side of the box, so that the 
spring can be pushed in place. There should be about 
yw inch space between the brass strip and the screw 
head, but this can be regulated according to the 
strength of the spring. For the push-button whittle a 
round end on a piece of wood the proper length and 
about J inch square. The round part should work 
freely in a hole through the box lid. 



no BOYS' BOOK OF ELECTRICITY 

For connections, bend a piece of wire under the screw 
head and solder another to the spring. Insulated bell 
wire should be used, with the ends scraped off clean 
where connections are made. Both wires can be 
brought out together through a hole in the side of the 
box. 

Batteries can be located near the bell or in the base- 
ment. The diagram in Fig. 74 shows the simplest 
arrangement of a bell circuit. 

If the* bell is to be rung from any one of several 
points other push-buttons may be wired in parallel. 
The circuit is then closed through the battery and bell, 
no matter which is pushed. 

A BURGLAR ALARM 

A burglar or chicken thief alarm can be arranged with 
the addition of a relay. Such a relay need have only 

Cut Here 




Fig. 85. — Bolt for magnet core. 



one coil, and is not hard to make. Its only purpose 
is to keep the bell circuit open as long as everything is 
all right, but to close it when a door or window is 
opened. 

For the relay magnet core an ordinary -j^-inch bolt 
cut off to 1 § inch in length can be used. It should 



ELECTROMAGNETS 



in 



be screwed in a strip of soft pine and fitted to the end 
of a sawed down cigar box, as shown in Fig. 86. A f- 
inch spool of No. 22 wire should be wound on a bobbin 
to fit, just as for the electric bell. No spring is needed. 
The armature should be hinged at one end, so that it 
will be held up as long as the magnet is energized. A 
clip should be bent from a piece of brass, so that when 
the armature drops it will be caught and a good con- 



| H1] I ^U ^^ 



- — m^ 



m. 



Fig. 86. — How alarm relay is wired. 

tact made. Two binding-posts should be attached 
above for the magnet circuit and two below for the 
bell circuit. To the upper posts the two ends of the 
coil are attached. From one of the lower ones a wire 
runs to the brass clip, and from the other one to the 
armature near the point where it is hinged. 

Suppose a chicken-house door is to be guarded. A 
thin strip of brass should be screwed to the top of the 
door, and another in the door casing, so that they rub 



112 



BOYS' BOOK OF ELECTRICITY 



together when the door is shut. To each of these a 
piece of insulated wire should be run. These should 



Wo Drh 







7b Dry\ 
Jell 
and Bell 



*eS 



Fig. 87. — Complete relay. 

be carried on insulators to the house, where connec- 
tion is made with the relay coil and battery in series. 




Fig. 88. — Wiring for a chicken-house door. 

This is a good place for a Daniell gravity cell to be 
used, as the circuit is closed most of the time. 
The electric bell can then be connected to a couple 



ELECTROMAGNETS 



113 



of dry batteries in a separate circuit. One wire from 
the bell and one from the battery should be connected 
to the lower binding-posts of the relay. It is well to 
put a little switch in this circuit, so that it can be opened 
in the daytime. If this is not done the bell will make 
itself a nuisance by ringing every time anyone goes into 
the chicken-house. 

One advantage of such a system is that the thief 
cannot stop the bell after it has once started ringing. 
If he finds the wires and cuts them the circuit will be 



Relay 




Door 



Gravity Cell 

Fig. 89. — Wiring for burglar alarm 



*?*" Bell 



opened and the alarm sounded just as if the door had 
been opened. The main disadvantage is that the 
alarm must be set by putting the armature in place 
every night. 



A THREE-CALL ANNUNCIATOR 

An annunciator is only a little harder to make than 
the burglar alarm. Much the same kind of materials 
are needed. It is necessary to wind three magnets 
instead of one. They can be of the same size as those 

8 



H4 



BOYS' BOOK OF ELECTRICITY 



for the alarm, and wound with No. 22 wire. Mount 
them on a §-inch board to which another board has been 




Fig. 90. — Magnets for annunciator. 



attached at right angles. In front of each one screw a 
piece of clock spring to which a soft iron armature 





Fig. 91. — Catch for an- 
nunciator drop. 



Fig. 92. — Three-call annunciator. 



has been riveted. The armatures may be made of 
i-inch sections sawed from the ends of the bolts which 



ELECTROMAGNETS 



ii5 



were used as cores. The springs should be long enough 
to almost touch the top of the containing box after 
they have been bent in the shape shown. A little hole 
for each should be cut near the top of the box, so that 
all will project through when not attracted by the 
magnets. 

Three little sliding doors or drops are now needed. 
These can also be made from cigar box wood. They 
should be about half the height of the box, and each 
less than one-third its width. 





1 

j 






4 3 t 



g 



Fig. 93. — Annunciator drop. 



Fig. 94. — Annunciator connections. 



Both for finish and to provide slides for the drops a 
piece of picture frame can be cut just to fit the box. 
Before this is put in place it can be fitted with three 
pairs of vertical wires; one for each drop. Tiny screw 
eyes or staples at top and bottom of the drops make 
excellent guides. 

Right under each spring tip a numbered card can be 
placed. When the drops are up all these numbers will 



n6 BOYS' BOOK OF ELECTRICITY 

be covered. When one of the drops falls the number 
behind is shown. Each magnet is made to work from 
a different push-button, and all the push-buttons are 
connected in circuit with the electric bell. 




Fig. 95. — Annunciator circuit. 

Only four binding-posts are needed for this annun- 
ciator. The connection is shown in Fig. 94. Connec- 
tions to both bell and annunciator are indicated in Fig. 
95- 

INDUCTION 

The circular lines of force that surround a wire when 
current is flowing in it are really tubes of force, since 
they extend the entire length of the conductor. The 
instant you connect the wire to the terminals of a 
battery these tubes begin to form. They grow from 



ELECTROMAGNETS 



117 



the wire to their full strength much as the rings of 
waves grow when a stone is tossed into a pond. When 
the current is stopped the process is reversed. Both 
movements are very rapid. 

If a second wire is put near the wire in which current 
is allowed to flow regularly, the lines or tubes of force 
will pass by it. When this happens an E. M. F. is 
induced in the second wire. It will be induced every 




Fig. 96. — Connections of an induction-coil. 



time the first wire is connected to or disconnected 
from the battery. 

This principle is used in the induction-coil. The 
wire is wound on a core of soft iron to make the best 
use of the magnetism. Current is interrupted almost 
instantaneously. 

While spoken of as a single coil, the induction-coil is 
really two separate coils of different sized wire. They 
are called the "primary" and "secondary" coils. 
The primary coil is the one connected to the battery 



n8 BOYS' BOOK OF ELECTRICITY 

which supplies the E. M. F. The secondary coil is 
the one which produces the spark. 

Just as with the two parallel wires, current from the 
battery has produced a varying magnetic field, the 
rapid changes of the field have generated an E. M. F. 
in the other wire. 

The E. M. F. of the secondary coil depends on the 
E. M. F. supplied to the coil, and on the number of 
turns of wire in each winding. If both coils are alike, 
the E. M. F. in primary and secondary will be the same. 
If the primary has a hundred turns and the secondary 
10,000, the secondary voltage would be 100 times that 
of the primary. With a battery of, say, six cells in 
series and ten volts applied to the primary, the second- 
ary E. M. F. would be 1000 volts. In an induction- 
coil the attraction of the primary core for a soft iron 
armature breaks the circuit, and a spring immediately 
closes it again. This is just what was done in the elec- 
tric bell. The action here is much more rapid. 

MAKING AN INDUCTION-COIL 

A good induction-coil is not an easy thing to build. 
Considerable care must be taken with each step, or 
the builder is apt to find that all his work has gone for 
nothing, and his coil is worthless. The wire used is 
thinly insulated and is very fine and easily broken. 
Any breaks must be very carefully repaired. One 
break would, of course, ruin the coil. 



ELECTROMAGNETS 119 

The induction-coil described here will give a spark 
1 inch long. This is large enough to make possible 
many interesting experiments, and can be used later 
for wireless telegraphy, where the distance is short. 



\ \ \ < 




Fig. 97. — Core of induction-coil. 

Requirements in the way of wire are a half-pound of 
No. 12 single cotton covered, and two pounds of No. 32 
single silk covered. For the core a bundle of No. 20 
annealed iron wire is used instead of the single rod 
needed for the bell and relay. These wires can be 




Fig. 98. — How wire is held in place. 

bought at any electrical store. About one pound will 
be needed. Have them cut 8 inches in length. 

To begin the coil make up a bundle of these iron 
wires f inch in diameter, binding both ends tightly with 
wire. Then wrap from one end to the other with two 



120 BOYS' BOOK OF ELECTRICITY 

layers of insulating tape. Now set the coil on end and 
pour shellac in between the wires. Allow this to dry 
before going any further. 

The primary, consisting of two layers of No. 12 wire, 
can now be wound on. This should be put on tightly 
and evenly. The beginning of this coil should be held 
in place by little loops of cloth as shown in Fig. 98. 
The winding should extend to f inch from one end of 
the core and to f inch from the other. Finish by wrap- 
ping the coil with ten layers of paraffined paper. 




Fig. 99. — Section winder for induc- 
tion-coil. 




Fig. 100. — Winding stand. 



While the secondary could be wound on the primary 
just as the bell magnet was wound, and insulated by 
layers of paraffined paper at every second turn, better 
results are obtained by winding the wire in sections. 
That is, the coil is made up of 12 sections slipped on 
over the primary winding. One big advantage of this 
is that every section can be tested as you go along. 

For easy winding a section winder should be made. 



ELECTROMAGNETS 121 

This is simply a flat spool with one end removable. 
The ends can be made from cigar box wood, and should 
be cut to about 3 inches in diameter. The center part 
on which the wire is wound should be i£ inch in 
diameter and \ inch thick. This should be turned on a 
lathe, but can be whittled out if proper care is taken. 

One end can be nailed fast to the center piece, but 
the other should be fastened by three screws, as it has 
to be slipped off after each section of wire is wound. 




Fig. 101. — How can and candle are fixed for winding sections of coil. 

A small wood shaft fitting tightly through the block 
provides the axle. A winding stand similar to the one 
made for the magnet coils is, of course, necessary. 

A second piece of apparatus will be needed for wind- 
ing the coil; this is a bath of melted pararfine. A 
square cake tin or a tin can big enough to hold the spool 
of wire will answer. If a tin can is used the lid must 
be soldered on and a hole cut in the side big enough 
to slip the spool of wire in. Both edges should be 



122 



BOYS' BOOK OF ELECTRICITY 



turned back to avoid scraping the insulation. The top 
edge can be used as a support. 

Enough paraffine should be put in the can to soak 
the coil, and it should be kept melted by a small candle 
set underneath. Be very careful not to get the par- 
affine bath too hot, it is liable to catch on fire, and 
besides the heat injures its insulating properties. 

To start the first coil of fine wire, pull the end of the 
paraffined wire through the small hole in the spool end. 




Fig. 102. — Coil section. 

Now turn the winding spool so that the wire will wind 
in the same direction as the turns on the primary. As 
the insulation is well soaked with wax, the coil will be 
quite solid when finished. The removable end of the 
spool can then be taken off and the coil pried out gently 
by inserting a knife between the windings and the wood 
end. In this way 1 2 coils should be made. Wind them 
all in the same direction. Three half-pound spools of 
wire should be enough to wind eight, though this 



ELECTROMAGNETS 1 23 

depends on the evenness of the winding. As each is 
finished it can be tested by putting the ends to the 
terminals of a dry battery. If a little spark can be 
made by rubbing the terminals the coil is all right. A 
test can also be made with a compass needle. 

After the 12 coils are finished, cut about 75 sheets of 
writing paper the same size as the coils and with a hole 
in the middle large enough to slip over the primary 
winding. Now make two square wood end pieces, 
boring a hole in the center of each large enough to fit 
the iron core and hold it tightly. Force the core into 
one of these wood ends, standing it upright. This is 
the first step in assembling the windings. Then slip 
on 4 or 5 sheets of the paraffined paper. Next comes 
the coil, put on so that its winding runs the same 
way as that of the primary. 

The next step is the most delicate and important of 
all. It is the connection of two coils. For convenience 
it is best to connect the inner end of the first coil to the 
inner end of the second. To do this the second coil 
must be put on so that its windings run opposite to 
those of the first. This allows the current to flow in 
the same direction in both coils. The two ends to be 
joined must be unwrapped and scraped very carefully. 
Then they should be united with a drop of solder and 
wound again with a fine silk thread. Before the coils 
are finally laid together slip four of the paraffined 
paper disks between them. 



124 



BOYS' BOOK OF ELECTRICITY 



The third coil is put on like the first. Its outer 
end is connected to the outer end of the second. 
Remember that the first, third, fifth, seventh, ninth, 
and eleventh coils are put on with windings running 




Fig. 103. — Diagram showing direction of coil windings. 

the same way as those in the primary. The second, 
fourth, sixth, eighth, tenth, and twelfth run in the 
opposite directions. Fig. 103 will give you an idea 
of the windings. Each coil should be insulated from 



\T: 




i\ 



o 



Fig. 104. — Interrupter parts. 

the next by at least four layers of paraffined paper. 
After the twelfth coil has been connected add enough 
paper sheets at the ends to fill the core within \ inch 
of the end. When the wood end is in place the core 
should come through it about yg- m ch. 



ELECTROMAGNETS 



125 




126 BOYS' BOOK OF ELECTRICITY 

You are now ready to add the interrupter. It is 
hard to make a good interrupter, so this part of the 
coil had better be bought. It can be secured from 
an electrical supply house. To connect it in after 
attaching it to the end piece with short screws, run 
one of the primary terminals to the vibrating part, 
and connect the contact screw to one of the binding- 




Fig. 106. — Tin-foil condenser. 

posts set in the coil base. The other primary ter- 
minal goes direct to the second binding-post. 

The secondary terminals are connected to another 
pair of binding-posts set on the end pieces of the 
coil. 

A spark could be secured from the coil just as it is 
now, but it would not be very long or very regular. 
There would also be a sparking at the interrupter 
point that would soon wear out the contact. To 



ELECTROMAGNETS 



127 



prevent sparking at the contact, and to give a longer, 
better secondary spark, a condenser must be added. 
For a condenser of suitable size, 100 sheets of tin- 
foil, each cut to 5 by 7 inches and left with a short 



Sea liner Wax 
Knob 



Brass 
Knobs) 




Fig. 107. — Spark gap. 

tab at one corner, will be needed. An equal number 
of sheets of good bond writing paper should be cut 
6 by 9 inches. In putting these together the tin- 



OTW~1 




Fig. 108. — Connections for induction-coil and spark gap. 



foil sheets should all be separated by the sheets of 
paraffined paper. Half of the little tabs should pro- 
ject from one corner of the package and the other half 
from the other corner. When finished bind each set 



128 BOYS' BOOK OF ELECTRICITY 

together with a piece of fine wire. The two wires 
make the terminals of the condenser. To connect 
it run one of the wires to the interrupter spring and 
the other to the bridge that holds the regulating 
screw. 

To hold the condenser a shallow box should be 
built under the base of the coil. A spark gap for use 
with this coil can be built from brass rods as illus- 
trated. Figure 108 indicates the connection for 
coil, condenser, and spark gap. 

WIRE TABLE 



American or B. & S. Gauge • 

"^ The resistance given in the table is that of pure copper wire; ordinary commercial copper haaa resistance from 
'.9 % -to 5# greater. 



Y" j. '.lag 


■'"■■' M. 


"J. 'Ml 






Gauge 


■' '■• :■ ,'"' : ' 




■$i 




Resistance of Pure Copper in Interuational 
Ohms at 20*C or 65 F. 


Diaro. in ) 
Mils ; , 


Area in Cir- 
cular Mils. 


Weight in tha, ' 
per 1000 feet 


Feet per 
Pound 


Wo. 


















Ohms per Ft. 


Feet per Ohm 


Ohms per lt>. <a 


'0000 


460.0 


211600. 


640 5 


1.56 


.0000489 


2044OT 


.00007639 


000 


4096 


167800. 


608.0 


1.97 


.0000617 


16.»10. 


.0001215 


>00 


364.3 


133100. 


402.8 


2.49 


.0000778 


12850. 


.0001931 





324 9 


105600. 


819.5 


3.13 


.0000981 


10190. 


.0003071 




289.3 


83690. 


253.3 


3.95 


.0001237 


8083- 


.000488$ 


:■* 


257.8 


66370. 


200.9 


4.98 


.0001560 


6410. 


.0007763 


j>i 


2294 


62630. 


159.3 


628 


.0001967 


6084. 


.001235 


§« 


204 3 


41740. 


126 4 


7.91 


.0002480 


■4031. 


.001963 


i* 


181.9 


33100. 


100.2 


9.98 


.0003128 


3197. 


.003122 


h 


162.0 


26250. 


79.46 


12.58 


.0003944 


2535.. 


.004963 


i* 


144.3 


20820. 


63.02 


15 87 


.0004973 


2011. 


.007892 


i» 


128.5 


16510. 


49.98 


20.01 


.0006271 


1595. 


.01255 


» 


114.4 


13090. 


39.63 


25.23 


.0007908 


1265. 


.01995 


10 


101.9 


10380. 


31.43 


31.85 


.0009972 


1003. 


.03173 


n 


90.74 


8234. 


24.93 


40 12 


.001257 


795.6 


.05045 


n 


80 81 


6530. 


19.77 


50.58 


•001586 


630.5 


.0802a 


13 


71.96 


6178. 


15.68 


63.78 


.001999 


500. 1 


.1276 


14 


64.08 


4107 


12.43 


80.45 


.002521 


396.6 


.2028 


(15 


57.07 


3257. 


9.86 


101.4 


.003179 


314.5 


.3225 


fM 


50 82 


2583. 


7.82 


127.9 


.004009 


249.4 


.5128 


I 


45.26 


2048. 


6.20 


161.3 


.005055 


197.8 


.8153 


40.SO 


1624. 


4»2 


203.4 


.006374 


156 9 


1.296 


19 


35.89 


1288. 


390 


256.5 


.008038 


124.4 


2.061 


S» 


31.98 


1022. 


309 


323.4 


.01014 


98.62 


8.278 


m 


28.46 


810.1 


2 45 


407.8 


.01278 


78.24 


6.212 


v» 


25^5* 


6426 


1.95 


614.2 


.01612 


62 05 


8.287 


23 


5 22 57 


509.5 


1.54 


648 4 


.02032 


49.21 


13.13 


M 


20.10 


404 


J.22 


817.6 


.02563 


39.0? 
30.95 


20.9» 


f*» 


.,,; 17.90 


320.4 


.97 


1031. 


.03231 


33.32 


26 


fc" 15.94 


254.1 


- .77 


1300. 


.04075 


24.54 


52.97 


27 


', 14.20 


201.6 


.61 


1639. 


.05138 


19.46 


84.23 


/M 


A\ 12.64 


159 8 


.48 


2067. 


.06479 


15.43 


133.9 


1 29 


A 11.28 


126.7 


.38 


2607. 


.08170 


12.24 


213.0 


JO 


,'.(: 10.03 


100.6 


.30 


3287. 


.1030 


9.707 


338.8 ■. 


! 81 


,ffl 8.928 


79 71 


.24 


4145. 


.1299 


7.698 


833.4 


32 


•j 7.950 


■63.20 


.1* 


6227. 


.1638 


6.105 


856.3 


iS3 


7.08$ 


60.13 


.15 


6591. 


.20BS 


4 841 


1361. 


! 34 


/ - 6.305 
j' 5.615 
\[ 5.000 


39.75 


.12 


8311. 


.2605 


3.839 


2165. 


1 85 


31.62 


.10 


10480. 


.3281 


3 045 


3441. 


( 3S 


25.00 


.08 


13210. 


4142 


2.414 


5473. 


»7 


l\ 4.453. 


19 83 


.06 


16660. 


.5222 


1.915 


8702. 


1 38 


■•■ 8.965 


15.72 


.05 


'21010. 


.6585 


1.519 


13870. 


*9 


{* 3.531 


12.47 


.04 


26500. 


.8304 


1.204 


22000. 


140 
■ >*4 


/*»•"* 


.9.69 


.03 


33410. 


• I Ml 


.955 


3*960.. 



ELECTROMAGNETS 1 29 

EXPERIMENTS WITH THE SPARK COIL 

With a well-made coil all the static spark experi- 
ments described in the second chapter can be per- 
formed. Many new ones are possible. When doing 
these always keep in mind that the voltage of the 
secondary is very high. A shock from it is not only 
very unpleasant, but actually dangerous. 

Experiments with the spark pane and filings burned 
by the spark make pretty exhibitions in a darkened 




Fig. 109. — A spark "ladder. 



room. To these the experiment with the climbing 
spark can also be added. The only additional ap- 
paratus needed is a small board provided with two 
binding-screws, and two pieces of fairly heavy copper 
wire. The bottom of these wires should be within 
sparking distance of each other, and the tops bent 
apart. When this spark gap is connected to the 
secondary of a coil sparks will continually jump 
across the bottom, climb to the top, and disappear. 



130 BOYS' BOOK OF ELECTRICITY 

With the glass bulbs known as Geissler tubes the 
induction-coil can be made to give a faintly flickering 
but beautiful light. These tubes are filled with rari- 
fied gases of different kinds and are made in a number 
of shapes. The plain ones are not expensive and can 
be bought from any electrical supply house. 

When the two metal ends of a Geissler tube are 
connected to the secondary terminals of a spark coil 



1 



m 



Fig. no. — Geissler tubes. 

it lights up in a very weird fashion. The color of 
light depends on the gas in the tube. Half a 
dozen different kinds hung around the wall and con- 
nected in series with the coil make a pretty decora- 
tive display in a darkened room. 

A somewhat similar effect can be secured with a 
burned-out incandescent lamp bulb. One in which 







131 



132 BOYS' BOOK OF ELECTRICITY 

the filament is broken gives the best results. By 
taking hold of the bulb and touching the brass plug 
to one of the secondary terminals the bulb is made 
to glow a faint ghostlike light. This can be seen 
only in a dark room. 

With a coil giving a longer spark experiments with 
X-rays may be performed. The X-ray tubes ordinarily 
cost in the neighborhood of from $5.00 up. They are 
simply tubes from which the air has been exhausted 
after platinum electrodes have been sealed in at the 
ends. The one in the small end is called the cathode, 
and the two in the bulb are the anodes. Rays from 
the cathode strike the diagonal anode and are reflected 
as shown in Fig. 112. These rays pass easily through 
flesh, but not so easily through bone. They will 
affect a photographic plate just the same as ordinary 
rays of light. 

If the anode is turned down a few inches above a 
plate holder containing a dry plate, and the rays 
allowed to strike it for a few minutes the plate is 
spoiled just as if it had been exposed to the light. 
If your hand is laid over the plate before the current 
is turned on you will get a shadow picture of the 
bones. The flesh seems to be transparent. 

This "shadow-picture" is not visible to the eye. 
A fluoroscope is needed to see the X-ray effect. The 
fluoroscope is simply a box covered at one end by a 
cloth coated with a platinum-barium-cyanide com- 



ELECTROMAGNETS 133 

pound. When the rays strike against this screen, it 
is all set in a faint glow. This can be seen by looking 
in the open end of the box. A hand held between 
the X-ray tube and the screen makes a bone shadow 
just like the one photographed on the plate. 

With a little practice very good photographs can 
be taken of hands, coins in purses, nails in wood, and 
a variety of other objects. 

In working with an X-ray tube it must be remem- 
bered that there is a right and wrong way of connect- 
ing it to the coil. This can be determined with the 
fluoroscope. If the connections are right the box 
will be filled with a greenish glow; if wrong, no effect 
is visible. Before changing the connection be care- 
ful to disconnect the batteries. 



CHAPTER VI 

Electric Heat 

A wire carrying a current of electricity always 
becomes heated. No matter how small the current 
is, some of the electrical energy is changed into heat. 
It is commonly said that this heat is generated in over- 
coming the resistance of the wire. A better way of 
imagining it is that when the little particles, or molecules, 
of the wire are set in such rapid motion by the current, 
they strike against one another until all become hot. 
There seems to be a mechanical action in the wire 
just such as you could apply on the outside of a rod 
by hitting it rapidly with a hammer. 

When a wire is carrying current the heat is radiated 
and carried away by the air. If all of this heat could 
be kept right around the wire so much would accu- 
mulate that the metal would melt. The time re- 
quired for this would, of course, depend on the current 
flowing. 

Each metal behaves differently as to heating when 

put in an electric circuit, just as it acts differently in 

other ways. Some have high resistance and melt 

easily, others have a low resistance and are quite hard 

134 



ELECTRIC HEAT 135 

to melt. Others have a high resistance and can be 
kept red hot for hours without a sign of softening. 

Copper has a low resistance, is fairly cheap, and has 
a high melting-point, so it is used to carry current. 
Alloys of tin and lead have a higher resistance and a 
much lower melting-point. Of these alloys "fuses" 
are made. Still other alloys have a high resistance 
and a very high melting-point. They are used to 
make electric toasters, flat-irons, and other heating 
appliances. 

Electricity is very easily changed to heat, but these 
resistance wires change it in such a way that it can 
be put at the useful work of ironing, toasting your 
bread at breakfast, boiling the coffee, and supplying 
heat any time for all sorts of uses. In all these heat- 
ing appliances you see the last step in changing sun- 
light back to heat. 

The coal at the power-house contains energy stored 
by the sun centuries ago. Unfortunately, the best 
engines and boilers made can only turn about one- 
tenth of that stored-up energy into electrical energy. 
Changing back is much easier, and every bit of elec- 
trical energy can be turned into heat. 

Whether the power you use comes from a water- 
fall or from a coal-burning plant, about the only 
difference between the electric heat it gives you and 
the natural kind sunlight furnishes is one of time. 
Sunlight is really stored up in the water and in the 



136 BOYS' BOOK OF ELECTRICITY 

coal. Where heat is obtained from coal many cen- 
turies passed by since it was stored up in the tropical 
plants; with water power the energy turned into heat 
today may have been spent only a few days before 
in evaporating water from ocean or lake. The water 
falls as rain, adds to the current that turns the tur- 
bine, and provides electricity to make your morning 
toast. 

All the electric heat we use today comes directly 
from sunlight in these two ways. Batteries for this 
purpose are too expensive and clumsy to be practical. 
To equal your electric heating circuit even for a short 
time at least a hundred primary cells would be 
needed. 

At ordinary prices for electricity, electric appliances 
are really economical. The heat can be applied just 
where it is needed and can be regulated perfectly. 
The demand has been so great that there are hundreds 
of these appliances on the market. A few are illus- 
trated in Fig. 113. 

In each of these the "heating element" is the im- 
portant part. This is simply a piece of high resist- 
ance wire connected in the circuit so that it will be 
heated by the current. By arranging its shape and 
size to suit, it can be made to provide just the sort of 
heat needed for each device. 

For the flat-iron the heating element must be flat 
and shaped to fit the bottom of the iron. In a toaster 



ELECTRIC HEAT 



137 





Heating pad. 



Chafing dish. 





Coffee percolator. 



Flat-iron. 





Radiant heaters. Electric toaster. 

Fig. 113. — A few electric appliances. 

the heat is radiated out to the bread instead of being 
held in by metal, so the wire is generally run in zig- 
zag coils. A still different arrangement is necessary for 



138 BOYS' BOOK OF ELECTRICITY 

the heating pad which takes the place of the hot- 
water bottle. In this the wires must be very long 
and very easily bent in all directions. They are en- 
cased with asbestos, which is both flexible and fire- 
proof, and the whole is covered with felt or flannel. 

With all these electric heating appliances electricity 
becomes as good a servant in the house as it is work- 
man in the factory. 

THE ELECTRIC FLAT-IRON 

An ordinary electric flat-iron furnishes a good ex- 
ample for the explanation of electric heating. Two 




Fig. 114. — Heating elements for flat-irons. 

insulated wires connect the power company's lines to 
the two brass prongs which usually stick out at the 
back of the iron. One of these prongs is connected 
to each end of the heating element. Both of them 
are insulated from the metal covering of the flat-iron. 
Flat-iron heating elements are made in many 
styles, though all of them are flat and shaped to fit 



ELECTRIC HEAT 139 

the bottom of the iron. Some zigzag back and 
forth, others are like a flat coil. In any case they are 
insulated from the rest of the iron by mica and as- 
bestos. To give the iron weight and make it hold 
the heat there is a piece of iron also above the heating 
element. 

There is not much that can happen to a heating 
element. Sandwiched between two pieces of iron 




Porcelain 

Tin Covering 



Connector 

Fig. 115. — One style of flat-iron connector. 

and protected by good insulation it will last for years 
under ordinary circumstances. If the iron should 
fail to heat for any reason, first make sure that the 
cord is all right by connecting it to some other heat- 
ing appliance. Each connection through the cord 
and iron must be perfect, as the current flows down 
one of the insulated wires through the heating element, 
and back again through the other wire to the power- 
house. 



140 



BOYS' BOOK OF ELECTRICITY 



If the cord seems to be all right, look for a break 
either in the flat wire that makes up the element or 
in the little wires that run to it from the posts. A 
more common place for failure in some irons is the 
plug that is used to connect the iron to the circuit. 
Sometimes the copper terminals become pitted by- 
sparking or the porcelain is broken. Repairs can be 
bought for either part. 





zm 

Fig. 116. — Three steps in making splice of flat-iron cord. 



When the cord wears out in a spot it should be fixed 
at once by splicing and winding each wire separately 
with insulating tape. Figure 116 indicates three steps 
in making such a splice. 

Never do any work on an iron when it is connected 
to the circuit. Carelessness in this is apt to result in 
a bad burn, or at least in blowing a fuse and cutting 
off your current. 



ELECTRIC HEAT 141 

A very common practice in using a flat-iron is to 
connect it right to a lamp socket. Sometimes the 
little key is used to turn off the current just as you 
would turn a lamp on and off. This is a very bad 
habit. If kept up the parts of the socket will soon be 
worn out by sparking, and a new lamp socket will be 
needed. A plug at the iron is provided to turn current 
on and off and ought always to be used. An addi- 



1 





Ri&ht Way 



YfronJ Way 



Fig. 117. — Push socket and plug. Fig. 118. — Right and wrong way of 

connecting wires. 

tional socket and plug at the other end of the cord is 
also a great convenience. 

Sometimes the wires become separated from the 
terminals in the plug or broken near it. When this 
happens, cut both wires off the same length, and then 
scrape off about \ inch of insulation. Fasten the 
wires firmly under the little screws and see that none 
of the fine wires stick out. When the flexible wire 
is- wound around the screw under the flat head, re- 
member to wind it in the direction the screw turns 



i 4 2 BOYS' BOOK OF ELECTRICITY 

when put in place. If this is not done the wire is apt 
to come out when the screw is tightened, or at least 
make a poor job. 

MAKING AN ELECTRIC TOASTER 

A plain but very useful electric toaster can be made 
from ordinary cement, using a simple mold made 
from a cigar box and two boards. The only parts of 
this toaster that need to be bought at the electrical 
store are a porcelain plug connector, about 6 feet of 
flexible cord, and 12 feet of resistance wire. After 
all the materials have been secured the first step is to 
cut the top of the box off so that the part left will be 
2 inches high all around. Then cut the cover down 
so that it is J inch narrower than the inside of the 
box and 1 inch shorter. For the next piece a bit of 
|-inch board is needed. This should be cut \ inch 
smaller all around than the cover was. With a sharp 
bitt put six equally spaced holes in one end of the 
board and seven in the other. 

To finish the mold a piece of board cut just to fit 
the top of the box is needed. Cut each of the corners 
off as shown in Fig. 119. Nail two strips across to 
prevent it from falling clear into the box when placed 
on it. 

In assembling the mold nail the piece of cigar box 
cover and the board with the holes together. The 
space should be the same all around the edge of the 



ELECTRIC HEAT 



i43 



thicker board. When fastening these two boards in 
the bottom of the box the holes should be up and the 
space at the sides even. Leave about twice as much 
space at the end with the seven holes as at the other. 
In this space the porcelain connecting plug will be 
held. Two holes in the middle of the box end will be 




Fig. 119. — Mold for casting cement toaster base. 



needed for the brass prongs of the connector to stick 
through. The fit should be good enough to hold the 
connector straight in place. 

The mold is now ready for the cement. If very 
carefully made there will be no trouble in getting the 
cement casting out of it. If each of the edges is 



i 4 4 BOYS' BOOK OF ELECTRICITY 

beveled a little and the whole inside of the mold 
treated with paraffine wax, a number of castings can 
be made if desired. 

Get good cement and mix it thoroughly. Before 
pouring, it is well to have 13 little pieces of cardboard 
ready, each the width of the small holes and one-half 
as deep. Set one of these on edge in the bottom of 
each hole. In pouring cement into the holes be 
careful not to disturb the position of these strips. 
The remaining quantity should be added slowly so 
that there are no air bubbles. The cement should 
be like a very thick paste. When the cement filling 
is within \ inch of the top press the top board down 
until the little strips nailed across it rest on the sides 
of the box. Some cement will squeeze up into the 
four triangular spaces left by the sawed off corners. 
If this is not enough to fill them level with the top 
of the box, add a little more cement and smooth off. 
This cement filling should be allowed to set for at least 
three days. 

To take the cement toaster base from the wooden 
form it will be necessary to pry the corners of the box 
apart a little. In removing the board with the holes 
a little more care is necessary. In each hole a small 
post is formed, and carelessness here might cause some 
of these to be broken. The small pieces of cardboard 
will be embedded in the ends of the posts, and when 
these are picked out little slots will be left. 



ELECTRIC HEAT 



145 



The toaster is now ready for the heating ele- 
ment. This should be made from 9^ feet of No. 26 
"Nichrome" wire if the lighting circuit is no volts. 
If it is 125 volts use 10 feet. Coil this wire tightly 




Fig. 120. — Cement base for toaster. 

around a small round bar (a small drill will do nicely) 
so that it is like a long spiral spring. Leave 3 inches 
straight at each end. Now pull it out evenly until 
the coiled part measures 6 feet. Connect one end to 



i 




gll*. a a t>_a &_<i-a-a-t> xi.n f> n .nj^ 


fCq^a^CLQ'a-n:.^ a a a a .a a.g.e.jt^ 


'<3aa.a.,a, a Q-a .a n n a -* n_a a_a a Ap, 


(j-a e; T$- n 0— p q ■% b; tf- e » u^"" ** ' 




*g a..n_B n a « 7» ra.-o — ft a a an n a a*\ 


gi-ifp e» o-b o » q «-g„u u q " g °i> "'" 


\P»-d- cUU»MUu«uu-«'»ua''''M" »" 





Fig. 121. — How the toaster is wired. 



one of the screws in the porcelain plug base in the 
cement, and run the wire in zigzag fashion from post 
to post. Connect the other end to the remaining screw 
of the terminal. The little slots that hold the resist- 



146 BOYS' BOOK OF ELECTRICITY 

ance wire in the posts may now be rilled with cement 
if desired to hold the wire more firmly in place. 

A piece of screening should now be cut to hold the 
toast. This should be of a size to just fit in the top 
of the toaster. By sandpapering and shellacking the 
outside of the toaster it can be given as nice a finish 




Fig. 122.— Screen for holding bread. 

as desired. It is very convenient and will allow you 
to toast your slices of bread in just a few minutes. 

OTHER USES OF ELECTRIC HEAT 

In addition to the household uses of electric heat 
there are many applications in factory work. The 
electric soldering iron saves the use of the blow torch 
and keeps a steady even heat as long as it is needed. 
The electric glue pot is largely used in furniture fac- 
tories. Electric ironing machinery in laundries and 
electric welders in iron working shops are quite com- 
mon. 

In the electric welder the two pieces of iron to be 
united form the conductor. Current is allowed to 
flow in them until they reach the intense heat neces- 



ELECTRIC HEAT 147 

sary for welding, they are then pressed or pounded 
together until they unite to form one solid piece. 
Rail joints of electric railway lines are often welded in 
this fashion, so that the whole line is one solid piece 
of iron instead of being broken by joints. 

Where an even more intense heat is needed the 
electric arc is used. This arc is the flame that is seen 
when the circuit carrying a heavy current is opened. 
Two carbons connected in a circuit and then pulled 
apart a little distance offer such a resistance the in- 
stant they are separated that some of the carbon is 
actually evaporated. This evaporated carbon carries 
the current, but has enough resistance to be kept at 
white heat and continually evaporates more of the 
carbon. The flame is white hot carbon vapor and air. 

The heat from this electric arc is so very intense 
that it will melt any metal known, and even makes 
possible the manufacture of tiny artificial diamonds. 
The electric furnace is used to make the grinding 
material called "Carborundum." This is almost as 
hard as a diamond, yet is made out of the simple mate- 
rials salt, sand, and ^sawdust by the application of 
electric heat. The materials are all mixed together 
and placed in a big electric furnace. After heat has 
been applied for some time the three common mate- 
rials have been changed to one of an entirely different 
nature. 

In a little different way the electric arc is used to 



148 BOYS' BOOK OF ELECTRICITY 

cut steel in buildings or bridges which are being torn 
down. For this work one of the electric terminals is 
firmly attached to the piece of steel and the other to a 
carbon tip furnished with a handle. Wherever the 
workman touches the tip of the carbon an arc will be 
formed and the iron quickly melted. Huge beams 
can be cut in a short time by this process. The job 
is not easy for the workman, as he has to wear heavy 
asbestos gloves to protect his hands, and double 
smoked glasses to keep the intense glare from blind- 
ing him. 

A small electric arc may be made with three or four 
primary cells and a couple of lead pencils. The ends, 
of course, must be notched so that the current from 
the batteries can reach the leads which are conductors. 
This experiment should be tried only with batteries 
and not with a lighting circuit. 



CHAPTER VII 

Electric Light 
a few facts about light 

Heat and light are a good deal alike. Both are 
caused by vibrations of molecules. At the tempera- 
ture called absolute zero, which is far colder than any- 
thing we know, all the molecules are supposed to be 
at rest. As soon as the material is heated at all the 
motion of these little particles begins, and becomes 
faster and faster as the temperature rises. Current 
passing through a resistance wire causes a motion so 
fast that the wire soon becomes too hot to touch. 
Then it takes on a glowing red color; it is beginning to 
give out some energy in the form of light. Increase 
the current and the color becomes brighter. Finally, 
there is a bright flash; the wire has actually melted. 

All the time the vibrating molecules are sending 
out waves of energy. At first these are felt only as 
heat. Next they affect the delicate nerves of the 
eye and we speak of them as light. The only way 
that we know these waves as light and heat is by 
their effect on our nerves of touch and sight. 

The nerves of the eye are so sensitive that they can 

even tell a difference between the length of waves that 

149 



ISO BOYS' BOOK OF ELECTRICITY 

are set in motion by the vibrating molecules. The 
different lengths give a sensation of different colors. 
Daylight shining on a piece of white paper or on clean 
snow has no color at all. It is really a combination of 
all colors. With a glass prism you could split these 
rays up into a rainbow, just as the light is divided 
naturally into a real rainbow. 

The light of a heated body is called direct light. 
When such light becomes bright it is painful to the 
eyes, which are intended for reflected light. The 
white rays from the sun strike on an object that we 
say is colored, and certain rays from that surface 
reflect into the eye, giving the sensation of sight. 
From a certain piece of paper all but the red rays are 
absorbed; the red is reflected. We say then that 
the paper is red. From another piece only the blue 
is reflected, and so on. 

An artificial light, to be pleasing, must have all the 
different colors in it. Then it is reflected the same 
as sunlight, and colors appear in their natural value. 

Nearly every one can tell colors easily. Brightness 
is much harder to judge. When you sit reading by 
an open window at sundown you hardly know that 
the light is getting dimmer and dimmer until, finally, 
you are unable to see at all. This is because the eye 
accommodates itself so very readily to differences in 
brightness. 

Guessing at brightness is a very poor way to tell 



ELECTRIC LIGHT 151 

whether a light is suited for reading or not. Manu- 
facturers, therefore, adopted a definite measure for 
it: This is the candle-power. A candle-power is the 
light given by a special kind of lamp burning a certain 
oil. Ordinarily carbon lamps were first made in 16- 
and 3 2 -candle-power sizes, as these were about 
right for reading and general lighting. Larger and 
smaller ones were soon added. The 16-candle-power 
lamp used about 50 watts of electrical energy and the 
pthers used more or less according to their size. At 
present the "rating" of a lamp is usually given in 
watts instead of candle-power. A 20-watt lamp, for 
instance, gives about 16 candle-power; a 60- watt lamp 
gives about 50 candle-power. 

THE ARC LAMP 

Before the incandescent electric lamp was per- 
fected the only available electric light was the arc 
light, which was not so very different from the arc 
lamp of today. In simple form the arc lamp con- 
sists of two pieces of carbon which are first touched 
together and then pulled apart so that current flows 
across the gap against a high resistance. One of the 
carbons in such a lamp is attached to each side of the 
circuit, so that current is forced through the carbon 
the instant their tips touch together. Heat is gener- 
ated immediately. The spot where the carbons 
touch becomes white hot. When the tips are pulled 



152 



BOYS' BOOK OF ELECTRICITY 



apart a little current continues to flow because con- 
nection is still made by the gaseous carbon and 
small particles of white-hot solid material that fill 
the gap. The temperature of the arc is so high 
(about 2000 F.) that the carbons are actually burned 
up. The intense light comes principally from the 
white-hot tips. 

The first man to really strike on the principle of 
the arc lamp was Sir Humphrey Davy. He turned 




Fig. 123. — Direct current arc. 

night into day in his laboratory, in 181 2, with one of 
the most expensive arc lamps that has ever been 
built. For current he employed a battery of 2000 
primary cells. His electrodes were two rods of char- 
coal, which he touched together and then pulled apart. 
The lamp was without regulating machinery and was 
simply fed by hand. Startling as this invention was, 
nearly sixty years passed before anybody really put 



ELECTRIC LIGHT 



i53 



the idea to work. Then a man named Jablochkoff 
created a sensation in Paris by lighting several streets 
with what he called an "electric candle," but which 
was only an improved arc light. 




Fig. 124. — A modern arc lamp. 

Jablochkoff's lights were bright, but would not 
burn long. Besides, they needed the services of a 
repairman to start them every time the current was 
interrupted. Improvements were needed and came 
rapidly. Clockwork was employed to feed the car- 



154 



BOYS' BOOK OF ELECTRICITY 



bons together as they burned, and thus keep an arc 
of the best length for proper lighting. 

Even this elaborate scheme was not very success- 
ful, and the solution, as often happens, was found 
in a simple method that is still used. A little clutch 
is operated by a solenoid so that the carbons are 
dropped together and pulled apart in just the right 
way to make up for the carbon burning away. When 



^7 



Solenoid 
Coih 

Solenoid 
Coih 




Fig, 125. — Principle of arc lamp. 



the circuit is actually broken, the light goes out for 
an instant. The solenoid immediately lets go of its 
clutch and the tip of the upper carbon drops to the 
tip of the lower one. Then current flows again; 
the magnetism of the solenoid pulls up a plunger that 
works the clutch; the carbons are separated, and the 
current continues to flow again in the white-hot 
gas. When the gap becomes too long the clutch 



ELECTRIC LIGHT 155 

lets go and the carbon drops again. This principle 
with variations is used in many lamps. 

As soon as it was perfected the arc lamp began to 
find a wide use. It supplied light to city streets, 
factories, warehouses, docks, mills, and wherever an 
abundance of bright light was needed. Its power- 
ful rays were well suited to the needs of search-lights 
on land and sea. Today it is used the world over 




Fig. 126. — Mercury- vapor lamp. 

in the thousands of moving picture machines, al- 
though in these installations the regulation is done 
entirely by hand. 

Another form of lamp somewhat similar to the 
arc lamp is the mercury-vapor lamp. In this the 
current is carried by mercury vapor instead of carbon 
vapor, the mercury being enclosed in a long vacuum 
tube. This lamp gives an excellent light for factories 



156 BOYS' BOOK OF ELECTRICITY 

and printing plants, but its color is not entirely pleasant. 
As the red rays are lacking from it, a greenish light is 
cast, which is disagreeable to some people. It is 
said to be very easy on the eyes in spite of its strange 
color, and is quite economical. 

THE INCANDESCENT LAMP 

Even if current had been cheap and common, there 
were several objections to the arc lamp. In the first 
place, it was entirely an outdoor light. Its bright- 
ness was too great for any such use as reading or 
house lighting. Another objection was that it used 
up carbons very rapidly and for that reason was quite 
expensive. 

When Edison began his experiments the important 
subject was called "dividing" the electric light. By 
this was meant dividing the great brilliancy of one 
electric arc into many little lights that could be used 
for reading and had about the same intensity or 
illumination as the gas flame or kerosene lamp which 
was then so generally used. Many scientists said 
the task was impossible and the search useless. One 
electrical authority claimed that the lighting of 
houses by electricity was "a mere dream," and that, 
therefore, all efforts in that direction were doomed to 
necessary and final failure. 

In the face of these discouragements Edison kept 
on experimenting. Every experimenter of those early 



ELECTRIC LIGHT 157 

days knew that platinum wire could be heated elec- 
trically until it gave out light. Edison's first trials 
were made with this wire. Platinum, however, was 
expensive and the light was very dim. Something 
better was needed. 

A story is told of the discovery of this improved 
material by Edison working one night in his labora- 
tory. Happening to roll between his fingers a bit of 
tar and lampblack, then used in his telephone, he 
was struck by the thought that this very substance 
might give a suitable light. Edison-like, he tried it. 
The result was surprising. It was not all that could 
be desired, but was much better than platinum. If 
carbon was good, why not try a carbonized thread? 
Putting a thread in an iron mold, he placed it in a 
furnace. This thread was placed in a glass globe. 
The air was removed so that the carbon would not 
burn. When current was sent through this slender 
thread the result was even better than before. The 
light produced was bright, yet soft and beautiful. The 
"division" of electric light had been accomplished. 

Other materials were tried. Experiments were 
made with paper, straws, cardboard, and hundreds of 
other substances. As delicate as the charred paper 
was, it seemed to give best results. Of this material 
the filaments were made which supplied light to 
Edison's grounds at Menlo Park more than thirty 
years ago. 



158 BOYS' BOOK OF ELECTRICITY 

With the same thin horseshoe of carbonized paper 
the very first independent electric lighting plant was 
equipped. This was on an ocean steamer, the 
"Columbia," which was built to run between San 
Francisco and Portland, Oregon. This little plant 
was put in operation in May, 1880, when the boat 
left New York for its long trip to the Pacific coast. 
Current was supplied by a generator built at Edison's 
factory. In spite of rough weather 'round the Horn, 
the delicate nature of the lamp filaments, and the 
newness of the whole thing, the plant on the steamer 
gave wonderful satisfaction. 

Subdivided electric light was now an assured fact. 
Developments came rapidly. Two years later, at 
Appleton, Wis., a small plant was built to generate 
electric power for distribution and sale. This was 
the first central generating station in the world, and 
quite a different affair from the enormous, powerful 
plants that supply electricity today. Its little Edison 
generator was turned by a water-wheel. 

Even the paper filaments which had been discov- 
ered after so much work did not satisfy the inventor. 
He experimented continually and searched the world 
for a better substance. Over 6000 materials were 
tried. Soon it was discovered that carbonized bamboo 
gave even a better light and lasted longer than paper. 
Filaments of other styles followed, each one better 
than the last. Today you read by a light that is the 



ELECTRIC LIGHT 



i59 




i6o 



BOYS' BOOK OF ELECTRICITY 



result of all these years of search and work. It is 
called the "Mazda" lamp. While the word "Mazda" 
was chosen by a number of manufacturers to indicate 
the best lamp for all time, the Mazda lamp of today 
has a filament of tungsten, and is sometimes called a 





Fig. 128. — Edison's first electric Fig. 129. — A Mazda lamp, 

lamp. 

tungsten lamp. Tungsten is a metal. It is very 
heavy, hard, and difficult to melt. 

Tungsten has a much lower resistance than carbon. 
For this reason quite a long filament is necessary. 
To provide for this extra length the wire has to be 



ELECTRIC LIGHT 161 

strung back and forth between supports in much the 
same way as the wire of the toaster already described. 
The glass rod in the middle merely supports the 
filament. 

There is one feature of these latest lamps that has 
remained just the same as it was in Edison's first 
paper filament lamp. This is in the way of bringing 
the wires from the outside through the glass. As 
explained, all the air is pumped from the lamp bulb 
before it is finished. The lamp has to be made so 
that all the air is kept out. In other words, the joint 
between the glass and the little leading-in wires must 
be absolutely perfect. Platinum has been found to 
be the only suitable material for this purpose. The 
reason for this is that it expands with heat exactly 
the same as the glass itself. If this was not true a 
little crack would soon develop where the wires pass 
through the glass, and the lamp would be ruined. 
Every year hundreds of pounds of platinum are 
used in the United States alone for the tiny wires 
that pass through the glass of incandescent lamps. 

Today the electric light has been "divided" further 
than even Edison thought possible. The electric 
flash-light, the electric lantern, and many applica- 
tions of incandescent lamps in smaller sizes can be 
made with the comparatively weak current of a 
primary cell. 



162 BOYS' BOOK OF ELECTRICITY 

MINIATURE LAMPS 

As comparatively high voltage is necessary for the 
larger lamps described, it is not wise to try any ex- 
periments with them. The smaller lamps mentioned 
will provide means of making a number of useful 
things. 

These lamps are made with carbon filaments and 
with tungsten wire filaments. The tungsten or Mazda 
lamps are better for all purposes, as they are both 




Miniature _ 

5 crew Candelabra Bayonet 

Screw Candelabra 

Fig. 130. — Miniature lamps. 



stronger and more efficient than the carbon type. 
Such lamps can be secured in all sizes from \ to 20 
candle-power, and for voltages between 1 \ to 20 volts. 
For use with one dry cell the ij-volt lamp should be 
used. Where more light is needed the 6-volt lamp 
operated by four dry cells in series is best. 

The smaller lamps are made with only one style of 
base, called the miniature screw base. The 6-volt 
lamps are commonly supplied with either the minia- 
ture base, the candelabra base, which is larger, or 



ELECTRIC LIGHT 163 

For any of these a 



the bayonet candelabra base 
socket to match is needed. 
An electric lantern is easily made with a 



-volt 



lamp and a single dry cell. This will give enough 
light to work around the barn or make trips to the 
cellar, and will be a great convenience. The first 





Fig. 132. — Switch for handle of lan- 
tern. 




Fig. 131. — Electric lantern. 



Fig. 133. — Pattern for reflector. 



thing needed is a box just big enough to hold a single 
dry cell. Put a hinged door at the back and provide 
a little catch to hold it shut. On the front screw a 
porcelain receptacle for a miniature base. From one 
of the contact screws run a wire direct to one battery 
terminal. The other wire should run right up the 
wire handle which is put on to carry the lantern. 



164 BOYS' BOOK OF ELECTRICITY 

The wooden grip of this handle should be wedged on 
so that it will not turn, and a spring switch fixed on 
the under side. From one side of the switch a wire 
runs to the battery, and from the other a connection 
is made direct to one lamp terminal. Ordinarily, the 
switch is open. In picking the lantern up you press 
the spring ends together and the lamp lights. This 
lamp is easy to carry and can be lighted and put out 
with one hand. There is no danger of setting things 
afire when you make trips to the woodshed or barn 
with such a lantern as this. A small tin reflector will 




Fig. 134. — Finished reflector for lantern. 

add to its efficiency, but, of course, is not absolutely 
necessary. 

A very nice present for a friend who is sick is an 
electric clock light. This can be made either with 
the one cell and a i|-volt lamp or four cells in series 
and a 6-volt lamp. The 6-volt lamp gives a much 
better light and permits longer use of batteries. The 
dry cells can be laid side by side in a box built to fit, 
and the miniature receptacle mounted near one end 
of the cover. One of the battery terminals and one 
of the socket terminals should be connected together. 



ELECTRIC LIGHT 



165 



To the other battery terminal and the remaining 
socket terminal connect the ends of a piece of flexible 
lamp cord. This can be of any length desired, and 
should have a pear push-button at the other end. A 




- — c<3> 

Push Buiton 



Fig. 135. — Night light for clock. 

reflector cut from a piece of tin and mounted back of 
the lamp adds to the appearance and effectiveness of 
the device. When a clock is set on one end of the 
box and the button pressed the dial is so brightly 



Sdt 



£C3> 



Fig. 136. — Wiring for night light. 

lighted that the figures can be read at quite a distance. 
It can be made as ornamental as it is useful by care- 
fully staining or shellacking it to suit the furniture 
of the room where it is to be used. 
Much the same scheme can be used to make a ruby 



i66 



BOYS' BOOK OF ELECTRICITY 



lamp for use in a dark room. In this, however, the 
lamp should be mounted at the back of the box, while 
the front is made up of a well-fitted piece of ruby glass. 
In this a switch which can be left on for some little 
time should be used. A very good switch for the 




Fig. 137. — Reflector for night light. 

purpose can be made from a piece of spring brass and 
two round-headed brass machine screws with nuts 
and washers to fit. Such a switch is illustrated in 
Fig. 138. 




Fig. 138. — Switch for dark-room lamp. 

Many other lighting appliances can be devised with 
a little thought by any boy who is handy with tools. 
Even tie pins can be whittled from bone and set with 
a little light inside. A little ingenuity makes ex- 
tremely pretty decorations possible for Hallowe'en 
parties, Christmas trees, and the like. The many 



ELECTRIC LIGHT 



167 



colors of the lights and their absolute safety makes 
them much better than candles for such a use. 

A table of some sizes in which miniature lamps may 
be bought follows: 



Diameter of Bulb. 
1^ inch 



T6 



f inch. 



Watts. 




Candle-power. 


Volts 


.6 






1 


1.5 


•75 






I 


2.8 


1.05 






I* 


3-8 


1. 05 
1. 65 






if 

2 


3-8 
6.2 


2.5 






2 


2 


1. 25 






I 


3 


2-5 
1.8, 2.5, and 


3.7 


1-S1 


2 

2, and 3 


4 
6 


5 
5 






4 
4 


4 
6 



CHAPTER VIII 



Electric Generators 



Before any great steps could be taken in electric 
power or electric lighting it was necessary to find a 
means of providing electric power in large quantities 
and at low cost. The primary cell was all right as far 
as it went, and even provided electric light — at a 
cost of $4.00 or more for burning one dim lamp an 
hour. Chemical energy could be converted into 
electricity in almost any quantity, but the process 
was too expensive to be used. The problem was 
solved when it was found that the power of an engine 
could be changed to electric power. In this way the 
energy was secured from the coal, and changed to elec- 
tricity through a steam engine and electric generator. 

Practically all of the power used today is secured 
from electric generators. Some of them run by steam, 
others by water power, but all are turning the heat 
of the sun back into electrical energy, so that it can 
again be used as power, light, or heat. 

In the electric generator swiftly moving wires 
passing through strong magnetic fields produce the 
E. M. F. that propels the street cars, lights our 
streets, and runs the factory machinery. This simple 



168 



ELECTRIC GENERATORS 169 

combination of a moving wire and a magnet is at 
the basis of the generation of all electricity today. 
The principle was discovered back in 1831 by Michael 
Faraday. 

Faraday long suspected that electricity could be 
produced from magnetism. He knew magnetism 
could be obtained from a battery current. For nine 
years he experimented, without result. He even 




Fig. 139. — Faraday's first generator. 

carried a little electromagnet in his pocket to help 
him think of his problem in spare moments. At 
last he succeeded in producing a slight effect by rapidly 
passing a loop of wire between the poles of a powerful 
electromagnet. Substituting a disk of copper for 
the wire loop, the inventor made a generator which 
he could turn with a crank. Current was taken of! 
by two brushes — one at the outer edge and one at 
the axle. This was the first generator ever made. 



170 BOYS' BOOK OF ELECTRICITY 

From this crude generator to one wound with 
many coils of wire was only a short step. Improve- 
ments have been mostly of a mechanical nature. 

An electric generator in the very simplest form 
can be made by placing a horseshoe magnet near the 
edge of a table and passing a piece of wire back and 
forth between the poles. The E. M. F. is too weak 
to be easily detected, but it is there all the same. 




Fig. 140. — How a weak E. M. F. may be generated in a wire. 



The invisible lines of magnetic force that pass from 
the North to the South Pole are actually divided or 
cut by the moving wire. The effect of this is to pro- 
duce the E. M. F. in the wire. Why this is so is a 
mystery; we simply have to accept it. 

There is no mystery about the direction of current 
or the voltage in any case. Both can be determined 
definitely. The E. M. F. depends on only two things: 



ELECTRIC GENERATORS 171 

the speed with which the wire is moved and the 
strength of the magnetic field. The calculation is 
rather complicated and cannot be gone into here. 
The matter of determining the direction is quite simple. 
The method is known as Fleming's right-hand 
rule. According to this rule the right hand is held so 
that the thumb and first two fingers point as shown 




lines 0/ Force 



Fig. 141. — Fleming's right-hand rule shows direction of E. M. F. 

in Fig. 141. If the first finger is pointing from the 
North to the South Pole, and the wire is moved in 
the direction indicated by the thumb, the E. M. F. 
will be in a direction pointed out by the second finger. 
With this rule the direction of E. M. F. is always very 
easily found. 
If a closed loop of wire is passed between the poles 



172 



BOYS' BOOK OF ELECTRICITY 



of a horseshoe magnet, a small current will flow in the 
direction indicated by Fleming's rule just as long as 
the wire is moving through the field. Pull the loop 
out again, and current flows in the opposite direction. 
This reversal of current is just what would happen 
if a dynamo was made from a loop of wire and two bar 
magnets as shown in Fig. 142. If this loop was 
turned round and round the E. M. F. would be first 




Commutator 



Direct 
Current 



Fig. 142. — A simple commutator. Every half-turn the current is reversed 
in the loop, but in the outside wires it is always in the same direction. 

in one direction and then the other, changing faster 
as the loop was turned with greater speed. This 
current would be very feeble, but otherwise practi- 
cally the same as the alternating current that oper- 
ates street lights and motors. It could be collected 
by a ring running to each wire. 

Although the alternating current generator is very 
simple, it was not popular at first because experimen- 
ters believed that only direct current could be used 



ELECTRIC GENERATORS 173 

to advantage. Their problem was to convert the 
seemingly useless alternating current to valuable 
direct current. This was done by using a simple 
device called the "commutator." Instead of having 
a ring connected to each end of the wire loop, a single 
ring was divided into two parts, and one-half con- 
nected to each end. This simple arrangement is 
shown in Fig. 142. The current still reverses in 
the wire loop with every half-turn, but it always 




Fig. 143. — Six-pole field winding showing magnetic circuits. 

flows in the same direction through the outside cir- 
cuit, which is the important thing. 

When these first dynamos were made permanent 
magnets were used to secure the necessary field. 
As a next step electromagnets were substituted. 
These were magnetized from a smaller dynamo 
made with permanent magnets. Then the discov- 
ery was made that a small part of the current gener- 
ated could be sent through the coils to keep them 



174 BOYS' BOOK OF ELECTRICITY 

magnetized. This principle is used in the shunt- 
wound generator today. Of course, some mag- 
netism is needed to begin with, or the generator 
would not produce any E. M. F. at all. There is 
usually enough magnetism left in the iron poles to pro- 
duce a slight E. M. F. when the armature is turning 
at full speed. This is called "residual magnetism.' ' 
The small current flowing through the field coils 





Fig. 144. — Shunt-wound generator. Fig. 145. — Series-wound generator. 



adds to the magnetism. This makes the field stronger, 
and a still higher E. M. F. is produced. Naturally, 
the E. M. F. is increased by this building-up process 
until the proper voltage of the machine is reached. 

Although the moving loop of wire and the mag- 
netic field are the important parts in a dynamo, 
there is a good deal more in an ordinary commercial 
machine. To begin with, there may be almost any 



ELECTRIC GENERATORS 



175 



even number of poles; suppose there are six. All of 
these are wound with fine insulated wire, so that 
when current is sent through the whole winding 
there is a North, South, North, South, and so on, 
clear around. The armature, which is turned so 
rapidly in the space between the poles, has a double 
purpose: the first is to carry the many coils of 
wire which pass through the magnetic field; the 




Fig. 146. — Compound-wound generator. 



second, to provide an easy path for the magnetic cir- 
cuits. The magnetic fields all stay perfectly still, 
but the wires held by slots cut in the iron armature 
are forced rapidly through one after the other of them. 
If the generator is a direct current machine the wire 
coils are fastened to the many separate copper bars 
of the commutator. Current then flows through the 
bars to the carbon brushes which press on them, and 
out in the circuit to do its work. 



176 



BOYS' BOOK OF ELECTRICITY 



A very small part of the current generated is used 
to excite the fields and provide the necessary mag- 
netism. This current can be provided in several 
ways, depending on how the coils are wound and con- 
nected. Shunt-winding is the simplest possible ar- 
rangement. In this the fields are in a separate 
circuit. Series generators have fields which are 
wound with only a comparatively small number of 




Collector 
Rings 



( = 

y At(ema1inff Current 

Fig. 147. — Simple loop with collector rings in place of commutator. 



turns. These fields are connected so that all of the 
current in the outside circuit flows through them. 
This is shown in Fig. 145. 

A third variety of winding is used in the com- 
pound generator. In this there are two sets of fields: 
one made of many turns of fine wire, and the other of 
a few turns of coarse wire or copper strip. This is 
the variety of winding which is most commonly used. 



ELECTRIC GENERATORS 177 

In an alternating current machine the main difference 
is that simple iron rings take the place of the commu- 
tator. These are called "collector rings." As reversals 
of current taken from these rings depends on the 
speed of the armature, the number of poles, and the 
winding of the machine, the frequency is usually 
spoken of when the voltage is given. By frequency 




Fig. 148. — An alternating current wave. 

is meant the number of complete reversals of direc- 
tion in a second. 

By twenty-five cycles we mean that the direction of 
the E. M. F. and the current has been completely 
turned around twenty-five times in a second. Sixty 
cycles means sixty complete reversals. Even twenty- 
five in a second sounds quite fast, but it is not fast 
enough for an incandescent light. The delicate 
filament cools off so much between reversals that the 

fight seems to flicker and is consequently unpleasant 
12 



178 BOYS' BOOK OF ELECTRICITY 

to the eyes. With sixty-cycle current no flickering 
can be noticed. 

Alternating current is becoming more and more 
popular for very good reasons. In the first place the 
machinery is much simpler than for direct current. 
A still greater advantage is that , the power can be 
sent, or transmitted, over long distances much easier 
than direct current. 

To understand this big advantage it must be re- 
membered that the power equals the voltage times 
the current. For instance, 10 volts X ioo amperes 
= iooo watts. This is just the same as i ampere 
at iooo volts. There is this difference: the single 
ampere at iooo volts could be carried over a very 
small wire, while the ioo amperes at 10 volts would 
require a much larger one. 

With direct current there is no simple way of rais- 
ing the voltage. If power is generated at no volts, 
it is transmitted over the circuit at no volts or even 
less. Alternating current, on the other hand, can be 
very easily raised or lowered to any value with a 
simple transformer. These transformers are con- 
tained in the iron boxes which may be seen on poles 
around a power-house or outside a factory. They 
work on much the same principle as the induction- 
coil, although there is no mechanical motion or 
breaking of the circuit. 

A transformer consists simply of two coils of in- 



ELECTRIC GENERATORS 



179 



sulated wire wound on an iron core. One of these 
coils is connected to the generator, and is called the 
"primary." The other is connected to the light or 
power line and is- called the " secondary." 

When the primary coil is connected to a generator 
supplying an alternating E. M. F. the iron core is 
magnetized. The magnetism is not steady; it grows 
and dies down many times in a second. With every 
change of strength the lines of magnetic force move. 
In their movement they are divided or cut by the 



\ary 



^»;wjmsjv;;sssa*sj>sx> 




'"■""■{SS SS-Q 1 



'Step Up 



Secondary 



m 



Primary < - ■ '\ 



tBZZZZZZZZZZZZZZZZZZZZ&k 



2ZZZZZZZZZZ& 



Step-down' 




Secondary 



Fig. 149. — How transformers are wound. 

wires of the secondary coil. Thus an E. M. F. is 
generated just as it would be if moving wires cut 
through a stationary magnetic field. If the number 
of turns on both primary and secondary were equal, 
the two voltages would be equal. If the secondary 
had ten times as many turns as the primary, the 
secondary voltage would be ten times the primary. 
If there were one-tenth as many turns on the second- 
ary as on the primary the secondary voltage would 
be one-tenth of the primary. 



180 BOYS' BOOK OF ELECTRICITY 

A transformer that is used to increase voltage is 
called a "step-up" transformer; a transformer used 
to decrease voltage is called a "step-down" trans- 
former. 

MAKING A DYNAMO 

The work of building a successful dynamo or gen- 
erator requires quite a little thought and a great deal 
of accurate work. Some lathe work, careful drilling 
and threading of holes, and at least one casting are 
necessary. It is useless to attempt the work of build- 
ing a dynamo unless the machine work on it is accu- 
rately done. In starting work on a generator the first 
thing to be made is the field structure. This can be 
made from two J-inch iron rods, a cross-piece of 
J-inch iron strip, and two pole pieces of wrought iron 
bar. The rods should be turned down to f inch at 
one end and threaded. They can then be passed 
through the holes in the iron strip and fastened by 
nuts. The pole pieces should screw onto the threaded 
bottom end of the rod and should be exactly parallel. 
The rods must stand at right angles to the cross- 
piece. The completed field structure should then be 
put in a lathe, and the pole faces turned until a cyl- 
inder i inch in diameter will just fit in. 

A little wooden armature should now be made 
just as shown in Fig. 150. This should be made 
very carefully, turned on a wood lathe, sandpapered, 
and then shellacked. It should be just a little too large 



ELECTRIC GENERATORS 



181 



X 

AliLU. 



<mnn> 



<nnn5 



ff— -— - — W: > 



h 



<3£ 



Wood Pattern 
for Armature. 




Finished Armature 



<• 



T\ 



Bearing -Commutator En<* Bearing -Pulley End 
Fig. 150. — Parts of dynamo. 




Brushes 



182 BOYS' BOOK OF ELECTRICITY 

to fit in the turned space. The pattern should be taken 
to a foundry where small castings are made, and a 
duplicate of the wooden form cast in iron. This 
should be turned down until it just fits loosely in the 
space at the bottom of the field structure. A hole 
should also be drilled to take the shaft. The shaft 
should be a straight steel rod and should fit so tight 
that it has to be driven in place. 

The next step is to bore a hole through a piece of 
fibre rod and force it onto the axle. The outside of 
this rod should be carefully turned down so that a 
piece of brass tubing can just be forced on over it. 
Fasten the tubing to the fibre by eight small screws 
carefully countersunk into the brass. Be sure that 
these screws do not go through the fibre and touch the 
shaft. The brass tube should now be sawed in two 
places. The fine saw cuts should go clear through the 
brass and a little way into the fibre. The armature 
is now ready to be wound. The winding is simple 
and consists only of putting on enough turns of No. 20 
cotton-covered magnet wire to fill the space left for it. 
Care should be taken not to put on so much that it 
will strike the magnet poles when the armature 
turns. Both ends should be brought out to the com- 
mutator, and one attached to each half with a drop of 
solder. 

For the field windings two spools are necessary, 
these being made to slip easily over the J-inch iron 



ELECTRIC GENERATORS 183 

rods. The ends should be made of cigar box wood or 
fibre, and should be about 1 inch in diameter. Wind 
these with No. 20 cotton-covered magnet wire, being 
sure to wind both in the same direction. After 
slipping the coils in place and bolting the yoke down, 
be careful that the field poles are exactly parallel, 
as they were when bored. 

Holes should now be bored and threaded in the 
ends of the two pole pieces, and two strips sawed out 
of sheet brass for bearings. One of these little strips 
can go straight across; the other should be bent to 
make room for the commutator. Especial care 
should be taken to see that the armature is centered 
perfectly, and does not scrape anywhere when it is 
turned. 

The dynamo is now ready to be mounted on a wood 
base. This should be about 3^ by 5J inches for the 
dynamo described. All that remains now is to add 
the brushes and make the necessary connections. 
The two brushes can be cut from sheet brass, and 
best as shown in Fig. 150. They should then be 
screwed down to the base so that one touches each 
side of the commutator. Now connect the two 
outside terminals of the field coils together, and con- 
nect one inner one to each of the brushes. Also run 
a piece of wire from each post to a binding-post. The 
wires can be run underneath the wooden base to give 
the work a neater appearance. 



184 



BOYS' BOOK OF ELECTRICITY 



The dynamo is now mechanically complete, but 
not ready to generate. It must first be connected up 
to two or three dry batteries in series and run as a 




o 
O 






motor. This magnetizes the fields and leaves a little 
magnetism in the iron. It must be remembered that 
this generator will only operate in one direction. To 



ELECTRIC GENERATORS 



185 



work as a dynamo it must be turned in the same 
direction as it ran when used as a motor. 




Fig. 152. — Wheel of windmill. 

To produce a high enough E. M. F. to light a small 
light the generator must be turned at a high speed. 




Fig. 153. — A wind-power dynamo. 

This can be secured by belting it to a large hand 
wheel, an old sewing machine wheel, or a little water 



i86 BOYS' BOOK OF ELECTRICITY 

motor. If a fairly steady breeze is available a small 
windmill of the "Jumbo" type can be used to supply 
power. This can be made from a drygoods box, 
and is much the same as an old-fashioned water-wheel 
except that wind instead of water forces the blades 
around. The size of the pulley wheel can be regu- 
lated so that the best results are obtained. Of 
course, such light will not be very steady, but it 
makes a novel wind-power electric light plant. 

BUILDING A TOY TRANSFORMER 

It is neither wise nor safe to try any experiments 
with an electric lighting circuit, or to attempt to run 
toys from it. Practically all toys are made to oper- 
ate at lower voltages and would be immediately ruined 
beyond hope of repair if an attempt was made to con- 
nect them to the no-volt lighting circuit. If alter- 
nating current is available the voltage can be reduced 
with a small transformer. Then the motors and toys 
designed for use with alternating current can be used 
with entire safety. With such a transformer minia- 
ture lamps can also be lighted. 

For a toy transformer large enough to run electric 
trains and motors the principal materials are a 
number of sheets of thin sheet-iron, about ij lb. 
of No. 22 single cotton-covered wire, and ij lb. of 
No. 12 double cotton-covered wire. 

The first step in construction is to cut out enough 



ELECTRIC GENERATORS 



187 



squares of the sheet-iron to make a pile 1 inch high. 
These should be 4 by 5 inches in size. Then cut out 







Fig. 154. — How sheet is cut for 
transformer. 



Fig. 155. — Transformer core. 



the middle of each sheet so that 1 inch of iron is left 
on each of three sides. By cutting a strip from each 
of the center pieces that are left a set of strips can 



I L < 

k i 



Fig. 156. — Spool end. 



be secured for the fourth side. Half of these should 
be cut to 3 inches and the remainder left the full 



i88 



BOYS' BOOK OF ELECTRICITY 



4 inches; i inch should also be trimmed off every 
alternate U-shaped piece in the pile. 

Now bind the two legs of the U-shaped set of 
pieces tightly with insulating tape, putting on two 
layers. They are now ready for the winding. Owing 
to the small number of turns it is hardly necessary to 
make separate spools, though this can be done if de- 
sired. In any case, four spool ends are necessary. 




Prim ary ' v Prima ry 

Fig. 157. — Transformer assembled. 



These may be made from fibre or cigar box wood that 
has been well shellacked. The four pieces should 
measure 2 inches square outside, and should fit tight 
on the legs of the transformer core. For the primary, 
600 turns of No. 22 cotton-covered wire should be 
wound on each leg. Both coils must be wound in 
the same direction. Bring the inside pair of ter- 
minals out through the small holes in the spool ends. 



ELECTRIC GENERATORS 



189 



The other ends should be connected together and 
the joint carefully wound with insulating tape. 

Over these coils should be wound two layers of good 
writing paper which has been well soaked in shellac. 
Let this dry before going ahead with the secondary. 
For the proper ratio the secondary winding should 
consist of 60 turns of the No. 12 wire on each leg. 
Wind the wire in the same direction as the primary. 
These coils should at first be put on somewhat loosely. 




Fig. 158.— How various voltages are obtained with toy transformer. 

A little slack will be necessary to add the taps properly. 
It is from these taps that current is taken at different 
low voltages desired. 

For the taps cut four pieces of flexible lamp-cord 
each about 6 inches long. For the first one, count 1 2 
turns from either end of the secondary. From the 
bottom of this turn scrape off a little insulation. 
Then wind about \ inch of the bare end of one piece of 
wire around the uninsulated part. A better job will 
be made if a little solder is used. 



igo BOYS' BOOK OF ELECTRICITY 

For the second tap count 24 more turns and con- 
nect another piece of the flexible wire; count 36 more 
and add a third. All of the joints should now be 
well covered with insulating tape, and the turns of 
the secondary wound tightly to finish the job. The 
end turns of both primary and secondary should be 
held in as described in Chapter IV. For protection 
and finish the coils may be wrapped in heavy black 
cloth which has previously been soaked in shellac. 

The only remaining work now is to make the base 
and arrange binding-posts and connections. The base 
need not be any certain size, but large enough to hold 
coils and core, leaving room at the end for the binding- 
posts. It should be made from good clear grained 
wood about f inch thick. 

For the primary side no binding posts are necessary. 
Connections can be made by bringing the two small 
wires down through the base and into grooves cut to 
receive them. Then bore a J-inch hole straight into 
the end of the base, and a f-inch hole up from the 
bottom to meet it. Then pass the end of a piece of 
lamp cord through the small hole and tie a knot in it 
1 inch from the end. Now solder the two coil ter- 
minals to the two wires of the cord, insulating the 
joints with tape, and laying the wires in little grooves 
cut for the purpose in the base. Put melted sealing 
wax in the grooves around the wire and around the 
knot in the cord. In this way all the strain is taken 



ELECTRIC GENERATORS 



191 




192 BOYS' BOOK OF ELECTRICITY 

from the transformer leads. Cut the cord to any 
convenient length and connect a standard screw plug 
so that current can be taken from any lamp socket. 

The secondary connections are somewhat more 
complicated. These too can be brought through to 
the bottom of the base if desired. 

Five binding-posts are needed, and should be 
equally spaced across the end of the base opposite to 
the primary terminal. To the two outside posts con- 
nect the two secondary terminals. To the three mid- 
dle ones connect the flexible leads in order. 




Fig. 1 60. — Bottom connections for transformer. 

Three wooden strips are now needed to fix the trans- 
former firmly on the base. These should be placed 
as shown in Fig. 159, the short pieces supporting the 
core ends and the long cross-piece being held down 
firmly by two long bolts. 

With the finished transformer carefully made as 
described you will be able to secure current at five 
different voltages from a no-volt 60-cycle alternating 
current line. These will be approximately as fol- 
lows: Between terminals 1 and 2, 1 volt; between 2 



ELECTRIC GENERATORS 



i93 



and 3, 2 volts; between 3 and 4, 3 volts; between 4 and 
5, 4 volts; between 2 and 4, 5 volts; between 1 and 4, 
6 volts; between 3 and 5, 7 volts; between 2 and 5, 
9 volts; between 1 and 5, 10 volts. 

With this range toy trains and motors can be run 
and miniature lamps of various voltages lighted. It 




Fig. 161. — Toy transformer with cover in place. 

should be remembered that the transformer is not 
intended to be left connected to the line. Disconnect 
it as soon as you have finished. Remember also it 
must not be connected to a direct current line. The 
direct current cannot be reduced to a lower voltage in 
this way, and the transformer would probably be ruined 
in the bargain. 
13 



CHAPTER IX 

Electric Motors 

"It's a poor rule," we say, "that doesn't work both 
ways." It would be strange indeed if heat could be 
turned into electricity and electricity could not be 
changed to heat. Since electric power can be secured 
from falling water, it is only reasonable to suppose 
that the state of affairs can be turned about, and 
water raised by electric power. Such changes of 
energy are everyday occurrences. Energy in one 
form is made to appear as another — and then changed 
back to its first form. The mechanical power of water 
falling over a cliff may generate electricity, and the 
electric power, carried to a farming district miles 
away, is put to work at the irrigation of orchards and 
farms. Of course, there is always a loss, but the 
convenience more than makes up for it. 

To generate this electricity the many wires of an 
armature winding are forced rapidly through a mag- 
netic field. The opposite way of the rule is that a 
wire carrying electric current will actually be pulled 
through a magnetic field. 

The truth of this is very easy to get at. All the 

apparatus needed, in fact, is a bar magnet, a couple 

194 



ELECTRIC MOTORS 



i95 



of dry batteries, and a piece of copper wire. Set the 
cells a couple of feet apart and connect the north pole 
of one to the south pole of the other. The wire 
should be fine, uninsulated, and long enough to hang 
rather loosely. Now stand a bar or horseshoe magnet 
upright under the wire and as close as it can be set 
without touching. With a second piece of wire touch 
the other two poles to complete the circuit. When 
current is allowed to flow there is an immediate 




Fig. 162. — This will show the principle of an electric motor. 

movement of the wire. It is pushed across the field 
even by the small current flowing. 

This action of a magnetic field on a wire carrying 
current was one of the discoveries made by Oersted 
in 181 9. Its importance is apparent, for every trolley 
car is propelled by this force, every motor of the 
millions that supply power to factories and shops is 
turned by the action of a magnetic field on a wire 
carrying current. 

When electric power was first used the simplicity 



196 



BOYS' BOOK OF ELECTRICITY 



of this principle was not realized. Inventors went 
the long way around. Devices called electric engines 
were built to operate on a magnetic or a solenoid 
principle. One experimenter even tried to run a boat 
with an engine of that sort. This strange craft ran 
on the river Neva in Russia and carried 14 passengers. 
Current from 320 Daniell cells propelled it at a speed 




Fig. 163. — Direct current motor. 



of three miles an hour — about the same speed as you 
ordinarily walk. 

Electric power uses were at this stage in 1861, when 
an Italian named Paconnoti discovered that an 
electric generator could be used very well and with- 
out any changes as an electric motor. He reasoned 
that since the dynamo produced electricity when 



ELECTRIC MOTORS 



^7 



rapidly turned, it should turn rapidly when supplied 
with electric power. This Italian was really the first 



7~ 




to see that if an ordinary shunt dynamo was con- 
nected to a circuit of proper voltage it would work 



198 BOYS' BOOK OF ELECTRICITY 

perfectly as a motor and change electrical power into 
mechanical power. 

For most people the motor is harder to understand 
than the generator. It seems quite natural that the 
mass of metal whirled by an engine should produce 
electricity or something equally wonderful. The 
hard thing to understand about the motor is where 
the powerful pull comes from, and how it can be so 
strong when the only points of contact between 
stationary and moving parts are at the carbon brushes. 
About the easiest way to imagine a motor is in the 
form of a single loop of wire turning between the 
north pole of one bar magnet and the south pole of 
another. Each end of the loop is fastened to half 
a metal ring. The two rings must not touch. This 
split ring is a simple commutator just as in the case of 
the dynamo. 

For bringing current through the loop two wires 
from the poles of a dry cell should touch the opposite 
sides of the ring. Current from the battery now 
flows up one wire, through one half of the ring, around 
the loop, and out through the other half of the ring 
to the dry cell again. When current flows through 
the coil it acts against the magnetic field and actually 
pulls one side of the loop up and pushes the other 
down. If the battery wires were spliced right on to 
the ends of the coil the loop would only turn a little 
way; then it would stop. It could not go on any 



ELECTRIC MOTORS 199 

more than water will run up hill. If the wires were 
reversed it would go on another half turn and then 
stop again. With the simple commutator shown, 
the current is actually reversed every half turn of the 
wire loop. There is really an alternating current in 
the revolving coil. But the result of it all is that the 
coil turns round and round if it moves fast enough to 
pass over the "dead center" each time. 

A very simple little motor which will make the 
principle clear may be built from a couple of hairpins, 
a needle, a good cork, and a few feet of fine insulated 
wire. 




Fig. 165. — Cork armature of motor. 

The cork should be even on the sides or should be 
trimmed so with a sharp knife. The knitting needle 
should be carefully forced through the exact center. 
Two entirely separate coils should then be wound on, 
both in the same direction, and with the same number 
of turns. At the end of the cork and in the spaces 
between the turns stick four straight pins. Each one 
must be the same distance from the knitting-needle 
axle. Scrape a little insulation from the end of each 
wire and connect the two ends of each coil to opposite 



200 BOYS' BOOK OF ELECTRICITY 

pins. The "armature" is now finished. For bearings, 
twist a little loop in each of two hairpins, sticking 
the ends in corks to act as supports. 

Now set the armature in its bearings between two 
magnets as shown in Fig. 166. It should spin around 
quite easily. To run it as a motor connect two fine 
wires to a dry cell, and hold the ends against opposite 
pins of the commutator. It may be necessary to help 



To\Ory$Cell 




Fig. 166. — Complete "cork" motor. 

the motor along a little at first, but once started it will 
spin along at a great rate. 

Of course, all large motors use electromagnets, and 
these are connected in the circuit in different ways, as 
they are for the shunt, series, and compound dynamo. 

In the series motor all of the current goes through 
the heavy copper field winding. In the shunt motor 
the coils are fine and there are many more turns, so 
that only a very small part of the energy goes to mag- 



ELECTRIC MOTORS 201 

netize the field. In the compound motor the greater 
part of the winding is shunt, but a few coils are wound 
on in series. 

The armature or revolving parts of all three kinds 
are practically alike. The wire is heavy and has very 
little resistance. If a big shunt motor was suddenly put 
in circuit there would be such a rush of current that its 
winding would be injured or perhaps ruined. When a 
motor is turning the movement of the wires takes the 
place of resistance and prevents this rush of current. 
So in starting, a motor field has first to be connected. 
Then a little current is allowed to flow in the armature 
through a starting resistance. As the motor speeds 
up the resistance is made less and less, until it is all 
out and the motor has the full voltage across it. 

It is now using very little current. Let it turn a 
pump, compressor, or any machine using power and 
enough current is taken from the generator to do the 
work. This current becomes heavier and heavier as 
work is added for the motor to do. In spite of all this 
load a shunt-wound motor keeps on running at very 
nearly the same speed. For this reason the shunt motor 
is best for pumping or turning lines of shafting where a 
regular, even speed is needed. To change this speed 
you would have to make the field weaker or stronger. 
A stronger field would make the motor run slower, a 
weaker field, faster. If the field connections were broken 
suddenly the motor would run so fast that the coils 



202 BOYS' BOOK OF ELECTRICITY 

would fly out of place and the machine would be 
ruined. 

In the series motor the speed is always changing. 
About the only use of this sort of motor is in hoisting 
work and on street cars. All street car motors are 
series motors. 

When a motorman starts his car he lets current flow 
from the trolley wire through his controller, through 
a resistance, then through the motor, and back to the 
power-house along the rails and ground. All of this 
current goes through the field coils of the motor as 
well as the armature. The field is enormously strong; 
the current in the armature is heavy. A strong slow 
pull is the result, and the car starts. Just as soon as 
it moves the current decreases. The field becomes 
weaker. The weaker field makes the car move faster. 
The motorman takes more and more resistance out so 
that soon the motor is getting all the voltage of the 
system. All the time the field is becoming weaker and 
the car is soon whizzing along. Even a moving car 
is hard to push, so there is soon a limit to the speed of 
the motor. Then it settles steadily to its work. If 
anything happened to the shaft — if the gears that 
drive the car should strip off — the motor would soon 
be going so fast that it would be ruined. Owing to 
this tendency to "run away" a series motor can never 
be run unless it has work to do to keep it at the proper 
speed. 



ELECTRIC MOTORS 203 

Very often a few turns of series winding are added 
to the shunt winding. These turns are put on oppo- 
site to the main field, so that the field will be weakened 
as the motor is loaded. This balances the natural 
tendency of a load to slow down the motor, and helps 
keep it at an even speed. 

While simpler from a mechanical point of view, the 
alternating current motor is more complicated elec- 
trically. The most common variety of alternating 
current motor is the induction motor. In this, current 
is induced in the armature coils by current in the 
stationary or stator windings. There are no field 
windings in the sense that there are on the direct cur- 
rent motor. 

MAKING A MOTOR 

A good motor can be made on exactly the design 
given for the generator in the preceding chapter. 
With even less work a simpler design can be made that 
will run along quite steadily, but with very little power. 

For the frame of this motor a piece of soft sheet-iron 
iVinch thick will do very well. It should be cut 
1 inch wide and 7 inches long. 

Then mark it with a file, or scratch it as shown in 
Fig. 167. These marks will serve as a guide in bend- 
ing. At A and B the strip should be bent at right 
angles. Then form the rounded part by bending care- 
fully over a f -inch rod, and bend back the two feet so 
that the frame is shaped to the form shown in Fig. 172. 



2o 4 BOYS' BOOK OF ELECTRICITY 

The field magnets may now be wound. For this 
purpose two layers of No. 22 cotton-covered wire will 
be sufficient. Before putting this wire on, each leg 



• — /&—»•* • +- /£"-» 


/«-* //«*-?" «-£-* 






°1 :: i !' -! 


1 I r. 

: n r 


I 




1 • 
• 1 


-*'?#? ^.#/%a- e<-/: 

£mkti 






\Ar mature 



Fig. 167. — Strips for frame and armature of toy motor. 

of the strip should be wound with a layer of insulating 
tape. After the magnets have been wound it is well 



^=gr 




Fig. 168.— Shaft of motor. 



Fig. 169. — Commutator. 



to test them by connecting the two free ends of the 
wire to the poles of a dry cell. A compass or an ordi- 





Fig. 170. — Commutator parts. 



Fig. 171. — Complete armature. 



nary sewing needle will tell whether the winding is all 
right or not. If so, the needle will turn sharply when 
current is flowing, or the sewing needle will be held 



ELECTRIC MOTORS 205 

across the two poles by the attraction. If the winding 
tests all right in this way it can be shellacked, which will 
protect it. 

Next comes the armature. This may be made from 
a strip of the same sheet iron that was used for the 
fields. Cut this also 1 inch wide and 2\ inches long. 
Mark off f inch from each end and turn the tips back 
as shown in Fig. 171. The two tips then point in 
opposite directions. Wind the straight parts with one 
layer of insulating tape. For the winding put on two 
layers of No. 22 cotton-covered magnet wire, the same 
as used for the fields. In putting this wire on it is a 
good plan to first mark the center of the strip by tying 
a white thread around it. Then begin the winding 
about \ inch away and wind to the bent part; then 
back to the start. Carry the wire over to J inch on the 
other side of the thread, and continue the winding in 
the same direction. On reaching the bent part wind 
back to the start. Be sure to leave a couple of inches 
of wire at each end for connection to the commutator. 
The winding can now be tested with a battery and the 
coils shellacked. 

For a shaft cut out two pieces of wood 2 inches long 
and trimmed down to \ x ^V inch. Cut a shallow 
mortise in each one so that the armature will be held 
tightly between them. Then set the armature in 
place even and true with a strip on each side, and tie 
the strips together with strong linen thread or fine wire. 



2o6 BOYS' BOOK OF ELECTRICITY 

A commutator may be easily made by bending two 
thin pieces of spring brass in half-round shape, leaving 
the ends turned in so that they will grip the wood. 
The shaft will need to be carefully rounded to receive 
them. A thin strip of wood forced between each 
pair of ends will keep the two parts separate, at the 
same time helping to hold them in place. 




Fig. 172. — Finished motor. 

When one wire of the armature is soldered to each 
of the sections the moving part of the motor is com- 
pleted. A needle forced into each of the ends of the 
wooden shaft makes bearings that have very little 
friction. 

Two bearing-posts can be very simply made from iron 
strips in which holes have been bored at the right 
height to hold the armature between the fields. These 



ELECTRIC MOTORS 207 

should be set in place temporarily to make sure that 
the armature is held at the right height, and does not 
strike on the field structure when rotating. The 
brushes still remain to be made. These can be cut 
from sheet brass and bent at the ends to touch the 
commutator. 

All parts are now in shape to be fastened with small 
screws to a wood base. The only connections neces- 
sary are made by bringing the two terminals of the field 
to the base of the brass brushes, and running a pair of 
wires from that point to a couple of binding-posts fixed 
to the base. 

This motor will always need a little assistance at 
starting, since it has only two poles and a very light 
armature. Some adjustment of the brushes may also 
be necessary. Even with these failings the little 
machine serves to illustrate the principle of the electric 
motor, and will spin along at a good speed if properly 
made on the current from a single dry cell. 



CHAPTER X 



The Telegraph 



In these days of wireless telegraphy we often lose 
sight of the importance of the older wire telegraphy. 
Experimenters have rushed to the extreme in building 
wireless stations, when often more satisfaction could 
be had among three or four friends connected by wire. 
The expense is much less and the chance to learn the 
proper use of the instruments much greater. As the 
simplest things should always be the first learned, it 
will pay any experimenter who is planning a wireless 
plant to first learn telegraphy with a Morse outfit. 

Although it is old compared to wireless, the Morse 
system is hardly old enough to be spoken of as "old 
fashioned," though some look at it that way now. Like 
the motor and generator, it had its beginning in the 
mind of Oersted in 1819, but the idea of sending mes- 
sages by the clicks of a magnetic armature was too big 
a stretch even for the imagination of those days. 

The possibility of sending messages did not even 
appear to Joseph Henry, who was the first to discover 
that an electromagnet could be controlled perfectly 

at a distance. Here was the germ of the telegraph, for 

208 



THE TELEGRAPH 209 

by closing the battery circuit a long way off the magnet 
was energized and would attract an iron armature. 
When the circuit was opened the armature would be 
released. The modern telegraph is really a growth of 
this idea that was worked out by the school-teacher, 
Joseph Henry, in his spare time. 

Henry's experiments interested Samuel B. Morse. 
Mr. Morse was a portrait painter. He had studied 
abroad under Benjamin West, and had become quite 
prominent. One of his characteristics was a good 
imagination. In his mind he saw that with Henry's 
idea signals might be sent like a flash of light for hun- 
dreds of miles, and perhaps, clear around the world. 

Professor Morse thought that the instrument ought 
to record the message in black and white, so he built 
his receiving instrument for that purpose. A strip of 
paper was moved along by clockwork, and each message 
was a string of straight marks, some long and others 
very short. When a message was finished the dots and 
dashes were translated into words. 

Morse's sending key was a heavy brass affair nearly 
two feet long. The relay magnets used were heavy 
enough to be a good load for two men. Compare all 
this with the neat little instruments that click out their 
messages in a modern telegraph office, and the won- 
derful improvements are quite apparent. 

Morse's first station, with these clumsy instruments, 
was not a great success. One end of the line was at 
14 



210 BOYS' BOOK OF ELECTRICITY 

Washington, D. C, the other at Baltimore. When 
completed in 1844 very few had faith in it. People 
bothered the operators with foolish questions and would 
not even send messages free of charge. Many jokes 
were told of the queer ideas many had about sending 
"letters by electricity.' ' So few were sent that the 
total receipts of the Washington office on one day were 
only 60 cents and on another day $1.04. From that 
first line with its small business to the enormous sys- 
tems of today is a mighty jump for the few years that 
have passed. 

About the first big improvement made was that 
operators began to take messages by sound instead of 
figuring the letters out from a tape. At first the little 
clicks were so feeble that it was hardly possible to hear 
them. Then the relay was devised, so that the sound 
could be made as loud as necessary at any distance. 
With one of these relays and a sounder in a little box 
near his ear the expert telegrapher can typewrite a 
message as fast as it comes in. 

PARTS OF A TELEGRAPH SET 

In an ordinary telegraph circuit for moderate dis- 
tances there need only be four parts; these are the key 
with which the message is sent, the sounder with which 
it is received, a battery to supply the current, and a line 
to carry it. 

The key is simply a contact switch that is held open 



THE TELEGRAPH 



211 



by a small spring. When the knob on the switch lever 
is pressed down, two little platinum points touch 
together, and the circuit is completed through the 
battery and wires to the other station. When the lever 
is allowed to come up again the points separate and the 
current stops. If the lever is held down for a very short 
time it makes what is called a dot. A longer space of 



Resfuiatinb 



3 crews 



Circuit 
Closer 




Knob 



Contact 

Tension 
Spring 



Fig. 173. — Standard type of key. 



time makes a dash. As the circuit has to be closed 
when the sender is not in use, there is a little switch 
attached for this purpose. Screws are provided so that 
the key can be adjusted to just the stroke that the 
operator finds easiest for him. 

A sounder is a little more complicated. Its most 
important parts are the pair of electromagnets and 
the soft iron armature that they attract. These mag- 



212 



BOYS' BOOK OF ELECTRICITY 



nets are wound with many turns of fine wire. The 
armature is held by a little spring at a short distance 



Regulating Screws 



Armature 



Anvil 




Fig. 174. — Combined key and sounder. 

above the poles. When current flows through the 
coils this armature is pulled down. When current is 




Fig. 175.— Relay. 

interrupted the spring pulls the armature away again. 
So every time the current flows there is a click — every- 



THE TELEGRAPH 213 

time the circuit is opened there is another. The click 
is made by a pivoted lever attached to the armature. 
Sometimes this lever is brass, in other makes it is 
aluminum. The two screws that it strikes can be 
regulated to suit the operator. 

A good key can be bought for about $2.00 and a 
sounder for a little more. Very neat sets with key and 
sounder both mounted on a base can be had for $4.00 
up. These are good for lines up to 15 miles in length. 
On larger ones a relay must be added. 

BATTERIES AND LINES 

For telegraph work the Daniell cell is the very 
best. On the other hand, it is somewhat wasteful, 
since zinc is being consumed all the time, as the 
circuit must be closed when the key is not in use. 
Where the line is very short and not used a great deal 
dry cells will do very well. If these are used the circuit 
must be left open; otherwise the cells would soon be 
worn out. For telegraph wire ordinary galvanized iron 
wire will do. This should be supported along the way 
by glass insulators so that the current will not escape 
to the ground. Only one wire is needed, which makes 
quite a saving if the line is a long one, as the ground or 
water pipes can be made to serve as a return. 

The simplest sort of a telegraph circuit is shown in 
Fig. 176. Connections are made so that the sending 
key at one end controls the motion of the sounder at the 



2i 4 BOYS' BOOK OF ELECTRICITY 

other. Every time the key is pushed down at one end 
the circuit is completed and the sounder at the other 
end is pulled down. Each time the key is released the 
sounder gives a second click. It is the time between 
the clicks that makes the dots and dashes. A quick 
pair of clicks is a dot. Clicks with a little more time 




Fig. 176. — How key and sounder are wired. 

between them make a dash. The letters made by com- 
binations of these dots and dashes are easily read after 
a little practice. 



A SIMPLE TELEGRAPH SET 

For a beginning it is a good idea to build a simple 
set of instruments, to telegraph from room to room, or 
perhaps from house to house, if another boy who is 
interested lives nearby. 

For such a set two keys and two sounders will be 
needed. The keys are quite easily made. A piece of 
board about 3x5 inches will serve very well as a base. 
On this mount a piece of spring brass, fastening it down 
by means of screws through two holes in the end. Just 
below the free tip set in a brass round-headed screw. 
A piece of tin bent in a U shape and screwed over the 



THE TELEGRAPH 



215 



brass spring should also be added. A hole may be 
punched through this and a small screw put in. Two 
small binding-posts should be attached to the base, and 
a wire run from one to the lower contact screw. The 
other connects to the base of the spring. This key can 
only be used with dry cells or other open circuit cells. 




Fig. 177. — A simple sending key. 

A sounder is somewhat harder to build. This in- 
strument is made up of two electromagnets mounted 
on a wood base, and placed so that an iron armature 




Fig. 178. — Field structure for tele- 
graph sounder. 



Fig. 179. — Coils of sounder in place. 



will be attracted whenever current flows through the 
magnet windings. The coils can be wound with No. 22 
cotton-covered wire. A couple of J-inch bolts will do 
very well as cores. The threaded ends should be 
screwed into a yoke and the heads cut off. Bobbins 



2l6 



BOYS' BOOK OF ELECTRICITY 



should be made just as in winding coils for bells. The 
four ends necessary can either be made from thin 
wood or from fibre board. After both coils are wound 
the magnet should be mounted vertically on the board 
base with a couple of screws placed through two holes 
in the yoke. Be sure that the magnet stands straight 
and true, and that the ends of the two cores are even. 

The armature can now be made. It should be cut in 
the shape of a cross from sheet-iron as thick as can be 
conveniently cut. Bore two holes in the long end of the 




Fig. 1 80. — Complete sounder. 

strip and fasten with screws to a block the same height 
as the electromagnet. If light sheet-iron is used a little 
of the tip should be rolled back or a little weight added 
to the tip. To balance this weight the armature should 
be supported by a rubber band or a light spiral spring. 
For the sounder points two screws should be set in 
a board at the proper height and the board screwed 
to the wood base. A little experimenting will show just 
where the points have to be placed to get best results. 
These points cause the clicks that produce the dot and 
dash alphabet. 



THE TELEGRAPH 



217 



To complete the sounder place two binding-screws 
at the end of the board and make the electrical con- 
nections. The two bottom leads of the magnet wind- 



u 



UT] 



Fig. 181. — Circuit with two keys and two sounders. 

ing should be connected together, and the two top ones 
should go to the binding-posts. 

With two sets built as described you can telegraph 
to your chum in the next room or the next house, using 




Fig. 182. — Combined key and sounder. 

the standard Morse telegraph code. The set illus- 
trates the principle of the telegraph and is built without 
much labor and at a very slight expense. An additional 
saving on wire can also be made by connecting the 



218 BOYS' BOOK OF ELECTRICITY 



points A and B, indicated in Fig. 181, to water or gas 
pipes, or to metal plates sunk in the ground. If ground 
plates are used they should be at least 2 feet square 
and should be sunk in ground that is always a little 



Regulating Screw* Pivot, 



/? . f gffij 



Contact 



£ 



m 




T 



9 



t ulatwf 
' 'Screvr 



To Bin ding Post fy ri/ Zf„ 

To Binding Posit 

Fig. 183. — Detail of key. 



damp. The damp ground or the metal pipes will carry 
the current quite as well as the wire. 

A combination key and sounder of a little more sub- 
stantial design is well worth while if much telegraphing 




( 



Brass Bar 



£ 



Soft Iron 
Armature 



Fig. 184. — Armature and anvil of complete set. 

is to be done. For this, a pair of magnets built the 
same as for the lighter set may be used. The heavier 
armature and sounder and the design of the key in 
detail are all shown in Fig. 182. It will be noted that 
a switch is provided in this outfit to close the circuit 



THE TELEGRAPH 



219 



when the key is not in use. The circuit on one set 
must always be closed to receive messages from the 
station at the other end of the line. A little different 
wiring is also necessary with this set. The general 
scheme is shown in Fig. 185. As arranged here the 
intention is to use dry batteries, and for that reason a 
small two-way switch should be connected in at each 
end of the line. One of these switches can be made or 







Ground .Ground 

Fig. 185. — Circuit for two key and sounder sets. 

bought at a very low price. When the sets are not in 
use these switches should be thrown so as to disconnect 
the cells, but keep the telegraph circuit closed. In 
this way the line is always kept ready for use without 
running down the dry cells. If gravity cells are used 
this little switch is not necessary, as the cells are in- 
tended for closed circuit work, and should be left con- 
nected in the circuit when not in use. If you and one 
chum are the only ones using your telegraph line, the 



220 



BOYS' BOOK OF ELECTRICITY 



instruments described, with batteries, are all you need. 
With a larger line, and five or six instruments, you 
would be fortunate in hearing the messages at all. This 
is where you would need a relay. One can be built in 




Fig. 186. — Two-way switch. 

your own workshop and is not much harder to make 
than a sounder. It is considerably more delicate and 
works with a very small current. The wire used for 
winding is very fine and there are many more turns than 
on the sounder. The armature is light, moves easily, 




Fig. 187. — A convenient ground clamp for water pipes. 

and is pulled through a very short distance. Each 
time it is attracted it closes a "local" circuit through a 
set of batteries and the sounder. The sounder then 
gives the usual loud click, while the relay is not heard 
at all. Wiring arrangement can be seen in Fig. 191. 



THE TELEGRAPH 



221 



Winding for the magnets is the same as in a sounder 
except that No. 32 cotton-covered or enameled wire 
should be used. 

The armature is made from a piece of ^-inch sheet- 




Wincfing 



Fig. 188. — Telegraph relay. 



iron. This swings in a frame made by bending a piece 
of sheet brass in a U shape. The two supporting 
screws can be ordinary machine screws with a little 




Fig. 189. — How relay armature is pivoted. 



socket drilled in the end of each. Two little L-shaped 

pieces of the same brass strip hold the screws that 

regulate the motion of the armature. (See Fig. 190.) 

A glance at Fig. 188 will show how the whole piece 



222 



BOYS' BOOK OF ELECTRICITY 



of apparatus is mounted on a little wood base, and how 
the connections are made. The middle binding-post 




Connected through 
frame to binding* 
Post 



To other 
binding post 

Fig. 190. — Relay contacts. 

is used only to fasten the spring or rubber band that 
pulls the armature away from the magnets. 
With two sets of keys and sounders two boys who 

Lint 




Ground 
Fig. 191. — Connection for receiving with relay. 

have plenty of enthusiasm can learn to telegraph in a 
short time. Care should be taken to begin properly, 
as bad habits in sending are easily acquired. They 



THE TELEGRAPH 223 

are much harder to get rid of and will limit the careless 
operator's speed. To begin with, the key must be held 
properly. The grip on it should be firm, but not stiff. 
One of the most widely used is known as the "Catlin" 
grip. In this the hand is held somewhat as in writing. 
The two forefingers are simply rested on the top of the 
knob, and it is not held at all. Some operators grip it 
lightly between the thumb and the second finger. 

For best results the key should be fixed solidly to the 
tables about 18 inches from the edge. This allows the 




Fig. 192— The "Catlin" grip. 

free wrist movement which is necessary. The forearm 
should rest on the table. There should be no side 
movement of the key in sending. For this practice 
a key sounder such as shown in Fig. 182 should be con- 
nected in circuit with a battery so that the beginner 
can hear the sound of his own letters. 

As a beginning the dots and dashes of the alphabet 
should be memorized with the help of the key. In 
practising the letters, it is well to learn the "dot" 
letters. first, then the "dot and space" letters, and then 
the "dot and dash" letters. 



224 BOYS' BOOK OF ELECTRICITY 

A single dot is made by a quick pressure on the key, 
so that it gives two clicks very close together. For a 
dash the lever is held down a little longer. A dash 
should take as much time as four dots. For a long 

THE MORSE TELEGRAPH ALPHABET 



A 


ft c 
■■••• •* • 






f 0' 


H 1 




J 


K 


i 


M 


N ;,/• O 




9 


V 


' » " i 


S 
••• 


T V 


V 


y» 




V 




& 




% 





NUMERALS 
• * J 4 

•■tone ••m«* •••■■• ••••■■ 

5 6 7 

■■■am •••••• san** *■•••• 

9. '' o^ 

PUNCTUATION 

Comm» Ptnod S*mi colon InUfOg^UeM 

Fig. 193. — Morse alphabet. 



dash, such as is used for the letter "L," the key should 
be held down for the space of six dots. 

For practice it is a good thing to make long strings 
of dots one after the other and all equally spaced. 
Then the dots in groups of 2, 3, 4, 5, and 6. These are 
the letters I, S, H, P, and the numeral 6. These should 
be perfected before going any further. 



THE TELEGRAPH 225 



DOT LETTERS 

E . H 

I . . P 

S . . . 6 



In sending these letters practice until the sounder 
clicks so rapidly that the "up-stroke" or " back-stroke" 
of the sounder is not heard. In the letter "P," for 
instance, the only back-stroke you could hear would be 
after the fifth dot. 

The dash letters are made by holding the key down 
for a part of a second before letting it up. The dashes 
in the letters should all be of the same length except 
in the letter "L." The dash for this letter must be 
noticeably longer than the others. 

DASH LETTERS 

L . T — 

M 5 

DOT AND DASH LETTERS 

N — • 

D — • • 

B — . . . 

8 — . . . . 

The above are the only letters which are made by 
starting with a single dash and then following with one 
or more dots. There should be no " back-stroke " 
15 



226 BOYS' BOOK OF ELECTRICITY 

heard until the end of each letter. A little thought will 
show why the dots should follow quickly. If the letter 
"N" was being sent, and a pause was left between the 
dash and dot, it would be read at the other end as 
"T I" instead of "N." A similar pause in sending 
"B" would change it to "T S." So the pauses mean 
just as much and are just as important as the dots and 
dashes. It is excellent practice to compare N and T E, 
D and T I, B and T S until you are entirely familiar 
with the sound of each. 

Further practice should be applied to the dot and 
space letters. These are as follows: 

DOT AND SPACE LETTERS 

c . . . o . . 

R . . . Y . . . . 

Z . . . . 

The space is made in each case by pausing a very 
short time between dots. There should be just enough 
pause to be noticeable. It is made by letting the key 
stay up for a fraction of a second, and recognized by 
the sound of the " back-stroke.' ' That is, the "back- 
stroke" will be heard after the second click of the "C" 
and after the first of the "R." As these spaced letters 
are considered the most difficult of all, they should be 
practised even more than the others. Compare the 
sound with that of the evenly spaced dots until you are 
perfectly familiar with each combination. 



THE TELEGRAPH 227 

After the alphabet has been learned, select a number 
of common words with the same endings or the same 
beginnings, and practice sending and receiving them 
until you are familiar with the sound of the whole word. 
It is best to have your friend far enough away so that 
there will be no temptation to call out to him to find 
out what he says or tell him what you are sending. 

A number of words and thoughts are very commonly 
abbreviated, and make telegraphing much easier when 
they are learned. A few of these follow: 



Min. 


Wait a minute. 


5 


Have you a message for me? 


7 


I have a message for you. 


8 


Wait, I am busy. 


13 


Understand? 


30 


Good-bye. 


Ga. 


Go ahead. 


Hr. 


Here is a message. 



In calling your chum at the other end of the line it is 
convenient to use the first letter of his name. His 
first name being George, you would send G several 
times until he answered. W 7 hen his attention was 
attracted he would answer by sending the letter I 
several times, and then signing or sending his initial 
G. You would then send the letters "Hr" and go on 
with your message. 



[CHAPTER XI 

The Telephone 

Receiving telegrams by sound instead of printed 
dots and dashes became popular just as soon as the 
instruments were perfected. Then men thinking along 
electrical lines began to wonder why other sounds could 
not be reproduced by wire in something the same way 
as the clicks are. All sounds are caused by vibrations 
or waves of some kind. The sound may be a click, a 
bang, a scraping noise, or a musical note; each one 
causes its own sort of motion in materials nearby. The 
wood sounding-board of a piano and the metal bell of 
a horn actually move when the instrument is being 
played. This movement can be plainly felt. It is 
very small and very rapid, but enough to make the air 
all around it vibrate strongly. The waves of air then 
strike on the ear-drum and give us the sensation we call 
sound. 

If the vibrations of the cornet bell could be dupli- 
cated electrically or in any other way the notes of the 
cornet would be reproduced. 

The movement of the telegraph key was recognized 

as a slow vibration. It was exactly reproduced at the 

228 



THE TELEPHONE 229 

other end of the line. If the key could be moved fast 
enough and the armature of the sounder was light 
enough to follow each movement, the result would be 
a humming sound at the sending end and receiving 
end. Both sounds would be exactly alike. For such 
a note to be produced at all the key would have to be 
moved about 34 times a second. If it vibrated faster 
the note would be clearer and sharper. It would go 
right up the musical scale until it reached nearly 
40,000 movements a second. Then it would be too 
high to affect the nerves of an ordinary ear. 

It occurred to a poor German named Philip Reis that 
a musical note might be sent by making vibrations open 
and close a magnetic circuit. He was without money, 
and his materials were beer barrel bungs, a sausage 
skin, and such bits of brass and wire as he could gather 
together. The skin was stretched over a hole and a 
bijt of brass attached to it touched a needle. When a 
note was sung or played near the membrane there was 
a vibration which rapidly made and broke contact be- 
tween brass and needle. This contact was connected 
in a circuit just as a telegraph key is. At the other 
end of his line was simply a battery and a small elec- 
tromagnet with a knitting-needle for a core. The 
magnet was mounted on a sounding-board. There 
was no armature, but the vibration of the needle core 
was enough to produce a sound. 

When middle C, which is always 517 vibrations per 



230 BOYS' BOOK OF ELECTRICITY 

second, was sung or played near the receiver of Reis' 
telephone it caused the circuit to be completed and 
broken 517 times a second, and the little magnet to be 
magnetized just as rapidly. The result was that the 
receiver gave out a faint note of the same pitch. But it 
made no difference whether the note was sung, played 
on flute, violin or cornet, the effect on the transmitter 
was the same. A listenercould not tell which was being 
played. Still, any note played near the transmitter 
reproduced, the same note in the receiver. 

Sometimes a word could even be understood, but 
Reis' telephone was apparently not much of a success. 

Receiver Receiver 

flUUT» lW/,i | 



(±*X 



Fig. 194. — How Bell's first telephone was wired. 

It remained for Professor Alexander Graham Bell 
to make the discovery that resulted in the wonderful 
systems of today. Bell had for many years been a 
teacher of the deaf. He knew the construction of the 
ear perfectly. He realized that the sound of the human 
voice was too complicated to be. reproduced by such a 
make and break arrangement. His solution was to 
place a little iron diaphragm very close to an electro- 
magnet to transmit the sound and another one just like 



THE TELEPHONE 231 

it to receive it at the other end. Then the vibrations 
in one diaphragm caused very delicate currents to be 
generated in the electric circuit. The other diaphragm 
was affected so that it vibrated exactly with it, and sent 
out sound-waves that were almost identical with those 
at the other end. Not only musical notes, but singing, 
talking, or any sort of sound could be heard. 

Of course, the little currents generated by the vibrat- 
ing diaphragm were weak. The telephones were only 
good for short distances. Then Professor Hughes and, 

Receiver 



Transmitter 




jmm 



Fig. 195. — Simple circuit with microphone transmitter. 

independently, Edison discovered the carbon transmit- 
ter that is used today. 

This depends on an altogether different principle. 
It is based on a device called the Microphone. Pro- 
fessor Hughes found that if two pieces of carbon touched 
lightly together a very slight pressure made a great 
difference in the resistance .at the point of contact. 
With two such sharpened pieces of carbon touching and 
each supported by a spring attached to a sounding- 
board very small noises could be heard. The footsteps 
of a fly .heard through an ordinary telephone receiver 



232 BOYS' BOOK OF ELECTRICITY 

connected in the circuit would sound like a horse gal- 
loping on a hard road. Even the very light steps of 
the fly are enough to affect the contact and change the 
resistance, so that the diaphragm of the telephone 
receiver is vibrated a corresponding degree. 

The explanation is that the slight pressure forces the 
molecules of the carbon tips together, and allows more 
room for the current to pass, with a consequently 
decreasing resistance. 

In the .modern telephone transmitter the material 
used is carbon broken into little grains, so that there 
are many delicate contacts in place of one, and a conse- 
quently greater effect. 

Here are the things that happen when you speak 
in the transmitter of a telephone: First, your voice 
striking against the iron diaphragm of the transmitter 
sets it into vibration, corresponding to every tone and 
change of the voice. With these vibrations a lot of 
little carbon granules are pressed together. Their 
resistance changes with the slightest movement of the 
diaphragm. As they are connected in the circuit the 
current flowing also changes rapidly. Thus every tone 
of your voice is faithfully followed by the changing 
current in the circuit. 

In the receiver at the other end this current flows 
through the fine coils of an electromagnet that is wound 
on the end of a permanent magnet. The tip of the 
magnet almost touches a soft iron diaphragm. All the 



THE TELEPHONE 233 

little current changes affect the magnetism of the little 
bar and, consequently, its attraction for the diaphragm. 
The result is that the diaphragm of the receiver vibrates 
exactly like the diaphragm in the transmitter. We 
hear — not the same vibration, that went into the trans- 
mitter — but brand new ones exactly like them. There 
is a great difference between this and Reis' scheme, for 







J § 










e* '<¥ 




W~*~-— ~ 


Damping" 




wm 






-• ' 'S v 


Jf ■*■ f 1 








* : 1 


1 - * 


jf ^-.. J 






1 --«* | 






K^-—-^ Moutt>p,ece 


'kVftM ^ ._ 




fir 
1 




>*^ Car bun 
~^9 ■ Sretiules 



Fig. 196. — Parts of modern telephone transmitter. 

the circuit is never entirely broken, and the tones 
reproduced are practically perfect. In the first tele- 
phone a middle C on all instruments sounded the 
same. With the modern telephone it is quite easy to 
recognize each one. 

The actual construction of a receiver and transmitter 
may be seen from the two sectional views (Figs. 196 and 



234 



BOYS' BOOK OF ELECTRICITY 



197). In the transmitter the main parts are the dia- 
phragm and the carbon contact arrangement. The 
grains of carbon are very hard and are especially pre- 
pared for the purpose. They are held between two 
highly polished plates of carbon. This transmitter is 
the result of great study and many improvements. The 



,. Magnet tof\ 


t V / Receiver ) 
k \_ / ^^- Cup ^gmsSC 


* 
Ear Pistes' r 




: /' ^^*^_ Permanent Ma&"et 



Fig. 197.— Parts of telephone receiver. 

receiver is practically in the same form as originally 
invented by Bell. 



HOW TO MAKE A TELEPHONE 

A telephone receiver is not hard to make, though it 
does require care in detail, and is very apt to be a 
failure unless the working parts are made accurately 
and correctly. The cost of making the receiver will 
be small, as the only materials to be bought are a small 
bar magnet, a hundred feet of No. 36 silk-covered wire, 



THE TELEPHONE 235 

and a piece of ferrotype plate such as is sold by photo- 
graphic dealers. The magnet should be about 6 inches 
long and not more than \ inch in diameter. 

The first step is to make a little spool for winding the 
fine wire. For this two discs cut from thin wood will 
be needed. They should be 1 inch in diameter and 
should fit snug on the end of the magnet. For the 
middle part of the spool wind a thin piece of cardboard 
or several turns of stiff paper tightly around the bar, 
and slip the two wood ends on over it. The ends should 





Fig. 198. — Spool for magnet Fig. 199. — Magnet and core for receiver, 
winding. 

then be glued to the paper center, so that J inch space 
will be left for winding the wire. When the glue is dry 
wind on the wire; leave 6 inches at each end for con- 
nections. To make the winding a little more solid it 
may be slipped off the magnet, dipped in a bath of 
melted paraffin, and slipped back again. 

This bar magnet and a little electromagnet, with a 
diaphragm of this iron held before it to produce the 
sound, are all the working parts of even the best tele- 
phone receivers. The rest is simply a case added for 
convenience and protection. A very good case to hold 



236 



BOYS' BOOK OF ELECTRICITY 



the magnet may be whittled from two pieces of wood, 
or, if a lathe is available, may be turned from a single 
piece. If two pieces are used they should each be 
whittled in the half-round shape shown in Fig. 200. 

If the wood is a straight-grained piece there will 
be no trouble in cutting the grooves for the magnet, 
wire, and air chamber A. The groove in which the 
magnet is held should be small enough to grip the steel 




Fig. 200. — Two halves of receiver case with magnet in position. 

bar tightly when the two halves are glued together. 
It should just be held with enough firmness so that a 
slight tap is required to move it. 

After both halves have been finished and fit together 
properly the magnet, with the coil in place, should be 
layed in the groove of one half and placed so that it 
lacks about -£% inch or even less of being even with 
the edge B-B. Then the two halves may be glued 
together and set in a vise or clamp to dry. 



i j 



THE TELEPHONE 237 

Two small binding-posts should now be set in the 
end, and one of the fine wires carefully soldered to each. 

The thin diaphragm should now be cut. One thing 
that must be especially remembered in doing this part 
of the work is to make sure that the part cut is perfectly 
smooth. There must be no dents in the diaphragm. 
It can be cut round with an old pair of shears, but the 
circle should not be marked on it with compasses. A 
better way is to mark and cut a piece of paper if inch 





0, 

Fig. 201. — Ear-piece and diaphragm. 

in diameter and then use this as a pattern for cutting the 
iron sheet. This avoids the little dent at the center. 

For a cap to hold the diaphragm in place a piece of 
J-inch wood can be used. A hole should be cut in it 
as shown in Fig. 201, and the bottom cut away slightly 
so as not to interfere with the free movements of the 
sheet iron, which is held all around the edge between 
the two pieces of wood. It should not be touched by 
the small wood screws which hold the cap in place. 

A little adjustment may be necessary to secure the 
best results. If the magnet is too far from the dia- 
phragm the sound will be weak, and if it actually 



238 BOYS' BOOK OF ELECTRICITY 

touches there will be no sound at all. The best point 
is where it just misses the magnet tip. With cap and 
diaphragm removed you should be able to see light 
between the magnet and a straight-edge held across the 
edges of the sound chamber. When this adjustment 
has been made and the cap fastened back in place the 
telephone receiver is complete. For the sake of ap- 
pearance it is a good scheme to paint it with lampblack 
or black paint and give it one or two coats of shellac. 
This receiver can also be used as a transmitter; thus 
a complete telephone line could be made with two trans- 




Fig. 202. — Complete receiver. 

mitters and a couple of dry cells connected in series 
between them. Such a line will not work well over long 
distances, but will enable you to talk between house and 
workshop or to your chum in the next block. 

Much better results can be secured with the carbon 
or microphone transmitter, which is now used in all 
telephones. As explained, this is not magnetic in 
action, but depends on changes of resistance caused 
when the sound-waves strike it. As a first step in build- 
ing a carbon transmitter cut out two pieces of carbon 
each xVinch thick and f inch in diameter, then bore 



THE TELEPHONE 



239 



a |-inch hole very carefully through the middle of each. 
Cut a circular diaphragm if inch in diameter from 
thin iron. This should have a hole in the middle and 
another at the edge. These carbon discs and the dia- 
phragm make up the principal parts of the transmitter. 
To fasten a disc on the diaphragm cut threads on 



Cordon 




©oiiiiitt m (©) 



® 

(HE 




Carbon 

Particles 



@ 



Cloth 




Fig. 203. — Parts and method of constructing telephone transmitter. 

pieces of |-inch wire and make nuts to fit, or buy small 
bolts sawed to the proper length. The next step is to 
break up some coke in pieces the size of a pinhead or, 
better still, secure from an electrical dealer about a salt- 
spoonful of the polished carbon particles used in the 
standard telephone transmitters. 



2 4 o BOYS' BOOK OF ELECTRICITY 

Cut a piece of cloth large enough to go around the 
carbon discs and lap over a little. Paste this two- 
thirds of the way around the two discs, leaving \ inch 
between them. Then drop in enough of the bits of car- 
bon to fill the space about two-thirds full. Finally, 
paste the cloth the rest of the way around. This 
makes up the working part of the transmitter. 

For the case, secure a piece of clear-grained wood i 
inch thick and saw out a block 2J inches square. In 




Fig. 204. — Back half of transmitter case. 



this bore a hole about -rw inch deep and just a little 
smaller than the iron diaphragm; bore a smaller hole 
deep enough to contain the carbon discs with their 
cloth wrapping, and a third § inch in diameter clear 
through the block. For the cover a piece of wood 
I inch thick will do. This also should have two sized 
holes cut in it; a ij-inch hole | inch deep and a 
i-inch hole the rest of the way through. Four holes 



THE TELEPHONE 



241 



for screws should be bored through the cover. The 
corners of both blocks may be trimmed as shown in 




Fig. 205. — Front half of transmitter 
case. 




Fig. 206. — Finished transmitter. 



Figs. 204 and 205. A small mouthpiece to collect the 
sound may be made from stiff pasteboard or tin, and 
the case assembled with the microphone inside. 





Fig. 207. — Section through assem- Fig. 208. — Detail of hook and con- 
bled transmitter. nection. 

The finished transmitter may now be made up either 

as a wall set or a desk set. For the desk set secure a 

piece of wood 8J inches long and about i inch in diam- 
16 



242 



BOYS' BOOK OF ELECTRICITY 



eter. A piece of broom handle will answer very well. 
Cut a J-inch shoulder at one end for the transmitter, 
and cut a mortise through about i inch below to receive 
the hook. This hook can be made from a single piece 
of brass as shown in Fig. 209. 

Two round-headed brass wood screws will serve as 
the two contacts, and a spring strong enough to nearly 
balance the weight of the receiver must be added. A 
piece of thin spring brass and a brass plate attached at 





To Upper 
Contact 

To Belt 



Fig. 209. — How hook is cut from one Fig. 
piece of sheet brass. 



To Line 



210. — Detail of bell-ringing 
switch. 



a convenient point on the standard make up a switch 
which closes the bell circuit of the other party and calls 
him to the line. In ringing up the other party with 
this telephone you first have to take the receiver off 
the hook and then press the little contact switch. 
Then the circuit will be completed through the hook, 
the lower contact of the hook, the batteries, and the 
line. Your chum's bell rings; he takes his receiver off 
the hook, and then both bells are disconnected — the 



THE TELEPHONE 



243 



batteries are in the circuit and you are ready to use the 
line. An ordinary electric bell with this battery ar- 
rangement will do all right as a signal for short lines. 




Fig. 211. — Desk telephone. 



For long ones a magneto is necessary to give a strong 
ring. 

In wiring the set built as described and illustrated by 
Fig. 211, it is well to bind all the wires together after 



244 



BOYS' BOOK OF ELECTRICITY 



connections have been made, and lay them in a groove 
cut in the telephone standard. This groove can then 
be filled with sealing wax. This little extra work adds 
both to the permanence and appearance of the set; 
when painted black it will have quite a workmanlike 
look if carefully made. 

THE MICROPHONE 

Many experiments have proved that an actual 
mechanical movement of the diaphragm is at the 



W 




*§ 



line. 



\3 



no 



Fig. 212. — One station of telephone circuit. Other station is exactly the 



bottom of telephony. The voice moves the diaphragm 
of the telephone to compress the particles of carbon in 
the transmitter. The sound-waves go from the mouth 
through air and strike the diaphragm, making it 
vibrate. 

In the instrument known as the microphone the 
sound comes through solid material instead of air, and 



THE TELEPHONE 



245 



is greatly magnified. This is the instrument which was 
discovered by Mr. Hughes, and independently by Edi- 
son. With it the experimenters were able to hear a fly 
walking about, and hear the buzz of his wings until it 
sounded like an express train. 

The microphone depends entirely on a very delicate 
contact between two or more conductors. They may 
be almost any conducting material, but carbon works 




Fig. 213. — A simple microphone. 



about the best. A very common form, illustrated in 
Fig. 213, is made with two bits of coke cut to about 
the size of dice and a sharpened pencil of carbon. In 
each carbon block bore a hole about ^g-inch deep with a 
sharp knife. A groove also will have to be cut in the 
lower block so that the carbon can be slipped in place. 
The little carbon strip can be made by taking the lead 
from a pencil and sharpening both ends to a fine point. 
Both the carbons can be glued to a little wooden stand- 



246 



BOYS' BOOK OF ELECTRICITY 



ard, and attached to a box made from thin boards. 
Much better results are secured if the box is glued in- 
stead of being nailed at the corners. A pair of small 
binding-posts should be added for convenience. 

With this microphone connected in a circuit with a 
couple of dry cells and an ordinary watch-case receiver 





Fig. 214. — Parts of watch-case receiver. 



you can hear the ticking of a watch very plainly at any 
distance you want to take the receiver. With a care- 
fully made instrument you can understand speech, hear 
music by setting it on a piano or graphophone, or do 
practically anything that can be done with a telephone 



THE TELEPHONE 



247 



transmitter. Adjustment to some extent can be made 
by tipping up one end of the box, which makes the 
carbon pencil lean heavier against the upper carbon 
block. 

With even less work a microphone can be made from 
a couple of safety razor blades mounted on a box. They 




Fig. 215. — Microphone made from safety razor blades. 

can be fastened on with a bit of sealing wax. When a 
piece of pencil lead is laid over the two sharp edges 
the instrument is ready for use. For convenience and 
to keep the lead from rolling off continually a piece of 



Metal 
Plate 




Metal 
Plate 



Fig. 216. — Multiple contact microphone made with broken coke. 

thin cardboard with a little slot cut in it to hold the 
pencil may be mounted upright between the two blades. 
The experience of the writer has been that this works 
the best of any easily constructed form of microphone. 
It transmits very nearly as well as a telephone. 



248 



BOYS' BOOK OF ELECTRICITY 



Another form which is easy to make, but not so deli- 
cate, is shown in Fig. 216. This is nothing more than 
a box of broken bits of coke. Current passes through 
it from a plate at one end to a plate at the other. It 
is really a multiple contact microphone of the sort 
used in a standard telephone transmitter. 

TELEPHONE INDUCTION-COIL 

All of these telephone and microphone arrangements 
transmit sound, but not always as steadily or clearly 

4- Layers *i<> 



ZO Layers *jz 



Fig. 217. — Induction-coil for microphone or telephone. 

as we would like. Some tones will be very good — 
others noisy or hard to hear. All are improved by a 



Primary 
Termina 




Secondary 
Terminals 



Fig. 218. — Finished induction-coil. 

very simple induction-coil. This consists of a J-inch 
iron rod 3 inches long wound with four layers of No. 16 
wire and twenty layers of No. 32 wire. The leads 



THE TELEPHONE 



249 



should be brought out to two pairs of binding-posts and 
the whole mounted firmly on a neat base. 




Dry CtU 
Fig. 219. — Connections of razor-blade microphone with induction-coil. 



m 



m 



"X 



?— 5. 



Switch 



To other station 



m 



Fig. 220. — Telephone circuit with induction-coil. 

When the primary of this coil is connected in series 
with battery and transmitter each change in current 



250 BOYS' BOOK OF ELECTRICITY 

makes a change in the magnetic field. Every one of 
these changes induces a current of much higher voltage 
in the many fine windings of the secondary. Conse- 
quently, each little change is magnified many times. 
When the receiver is connected in the secondary there 
is a great gain in loudness and clearness of tone. The 
small work of making this little coil is well paid for 
by greatly improved results. 

The wiring for an induction-coil in a microphone 
circuit is shown in Fig. 219, and for a telephone circuit 
in Fig. 220. 



CHAPTER XII 

Wireless Telegraphy 

When you sit in a quiet room and watch some one 
blowing smoke rings you have about the best visible 
example of the way wireless messages travel. The 
ring starts in a little puff of smoke and whirls in a wider 
and wider circle. The next ring follows — then another 
and another. If they were timed in dots and dashes a 
message could actually be sent across the room in 
smoke. In wireless, a series of waves or disturbances 
are similarly started by a heavy spark ; they spread out 
and out through a substance called " ether" which fills 
all space. Ether is an actual substance, yet colorless, 
odorless, and almost without weight. It is so very light 
that a mathematician has estimated the weight of a 
sphere the size of our earth at only 250 pounds. The 
word " ether" is said to be derived from a Greek word 
which means the same as our term "perpetual motion." 
The ether is supposed to be in constant motion. 

Vibrations set up in this substance by the sun's 
energy appear on the earth as light and heat. Light 
is brought to us by it at the speed of an electric current 
— 186,000 miles a second. At the same speed and in 
much the same way the disturbances or waves used for 

251 



252 BOYS' BOOK OF ELECTRICITY 

wireless are carried through it. These are called electro- 
magnetic waves, or " Hertzian' ' waves, after their 
discoverer. 

All wireless messages are sent with Hertzian waves. 
These travel from the spark in much the same way as 
the smoke rings did, or the tiny ripples that move from 
the center of a tub of water when a pebble is dropped 
in it. In Fig. 221 the spark is represented by the 




Fig. 221. — Ripples on water resemble electromagnetic waves. 

pebble and the ether by the water. Messages could be 
arranged just by timing the ripples and making them 
into dots and dashes with spaces between. Just as the 
ripples go in all ways from the center of the tub, the 
electromagnetic waves move in every direction from 
the spark which starts them. A message sent from 
Detroit to Chicago, for instance, would reach Mackinac 
on the north, Rochester on the east, and Cincinnati 



WIRELESS TELEGRAPHY 253 

on the south all at exactly the same instant and with 
equal strength. 

As so little of the energy ever reaches any receiving 
station, a strong spark is quite necessary for sending. 
This might be produced with a static machine, an induc- 
tion-coil, or a transformer. The first is never used for 
the purpose on account of unreliability and other fea- 
tures which are not desirable. For small sets an 
induction-coil such as is described in Chapter V does 
very well. 

A sending set of the simplest kind would consist of 
such a coil with a telegraph key and batteries connected 
in the primary, and a spark gap in the secondary. One 
side of this spark gap is connected to an aerial, consist- 
ing of several wires strung at some height from the 
ground; the other is firmly connected either to a ground 
plate or to a water pipe. 

This is the way such a set works: The moment the 
key is closed the E. M. F. of several thousand volts 
is generated in the secondary. The aerial and ground 
are instantly charged. As soon as this happens a spark 
jumps across the gap, and the electromagnetic waves 
start off at lightning speed in all directions. A touch 
of the key sends out the few waves that make a dot in 
the code, and holding it down a second makes a dash. 
Either the Morse or Continental code could be used. 
For reasons to be given later this simple "hook-up" 
is forbidden by the United States wireless laws. 



254 



BOYS' BOOK OF ELECTRICITY 



When the swiftly moving electric waves pass a wire 
a current is generated. If this wire is near the start- 
ing-point there will even be enough induced to make 
quite a heavy spark. At a distance of several miles 
the waves have spread so that the effect becomes very 
weak. There must be quite a long wire to catch enough 
for a signal. The aerial wires that indicate the houses 



InductlQ^k 
Coil 




Fig. 222. — Simple transmitting set. 

and workshops of so many wireless experimenters are 
as important for receiving as they are for sending. 

Even with these long wires raised high in the air the 
effect of the transmitted waves is very feeble. If the 
distance between the' two stations is many miles, only 
a very small part of the original energy ever reaches 
even the longest of aerials. The rest is wasted as far as 
the receiving station is concerned. The problem is to 



WIRELESS TELEGRAPHY 



?55 



read dots and dashes from such a very small disturbance. 
For this a telephone receiver is generally used, and, as 
delicate as it is, it cannot do the work alone. In addi- 
tion, a detector is needed. The object of this is to 
change the very small oscillating currents that come 
from the aerial into direct current. It then affects 
the telephone receiver so that a sound is produced. 
There are several metals and ores from which detectors 




petector 



Fig. 223. — Simple receiving station. 

can be made. Among these are silicon, galena, and 
iron pyrites. Both galena and fused silicon give ex- 
cellent results and are commonly used in very easily 
made detectors. 

The simplest arrangement of a receiving station is 
shown in Fig. 223. It consists merely of a detector 
connected in the line that runs from the aerial to the 
ground, and a telephone receiver connected across the 
detector. 



256 BOYS' BOOK OF ELECTRICITY 

When electromagnetic waves from any source pass 
by the aerial they generate slight oscillating currents. 
This flows to the ground through the detector, is recti- 
fied by it, and heard as a faint "buzz" in the receiver. 
There are no clicks of the sort heard with the Morse 
telegraph sounder. 

In theory the simple sending and receiving set de- 
scribed would send messages over short distances fairly 
well. In practice their use would be impossible, as the 
untuned transmitter is stricly forbidden by United 
States wireless law. A simple tuning arrangement not 
only complies with the law, but enables you to trans- 
mit messages over much greater distance. By "tun- 
ing" is meant a regulation of the oscillating discharge 
of the system so that the electromagnetic waves are 
greatly increased in strength and only one length of 
wave is sent. The action of a tuned transmitting set 
resembles that of a bottle made into a whistle by blow- 
ing over its edge. You may blow hard, soft, at any 
angle, but the tone is always loud and clear on some 
particular note. The sound-waves of this note are 
added in the bottle in such a way that its loudness is 
greatly increased. 

An idea of a single wireless wave may be gained from 
a simple experiment with a rope or heavy cord. Tie one 
end to a post and shake the other in a way sailors call 
" Surging. " Wave after wave can be made to run along 
to the post. The line moves only up and down; the 



WIRELESS TELEGRAPHY 



257 



wave travels lengthwise. As the line is shaken more 
rapidly the waves become shorter. Moved more slowly, 




Fig. 224. — Wave motion is easily shown with a long piece of rope. 

they become longer. By wave length is meant the 
distance from the top of one wave to the top of the 
next. 




Ground Fixed Condenser 

Fig. 225. — Receiving station arranged for tuning. 

Wireless waves traveling in ether may be almost any 

length. Those starting from a flash of lightning may be 

as long as 10,000 miles. At the other extreme waves 

have been produced which must be measured in ten- 

17 



2 5 8 



BOYS' BOOK OF ELECTRICITY 



millionth parts of an inch. By reason of the United 
States wireless law now in force amateur stations are 
not allowed to use waves longer than 200 meters. A 
meter is a little more than a yard. 

With a receiving station also tuned to catch the re- 
inforced waves of the sending station great distances 
are possible. The circuit is only sensitive to one length 




Dry Celts 



Ground 



Fig. 226. — Tuned transmitting set, close coupled. 

of wave, and so disturbance from other stations is 
avoided. 

A sending station is tuned by putting a "helix" 
and condenser in the circuit. This helix is simply a 
coil of wire mounted in a frame and provided with 
contact clips for ground and coil. It is connected be- 
tween the aerial and ground as shown in Fig. 226. The 
condenser is connected between the spark gap«and helix. 



WIRELESS TELEGRAPHY 



259 



With these additions the outfit becomes a simple tuned 
transmitting set. It is " close coupled," which means 
that the secondary of the induction-coil is actually con- 
nected in the aerial circuit. Adjustment or " tuning" 
is secured by changing the position of the two clips A 
and B which make contact with the metal of the helix. 




Ground 
Head 5et 
Fig. 227. — Tuned receiving set, loose coupled. 

Even better results in transmitting can be secured 
with an oscillation transformer put in place of the 
helix. The arrangement in Fig. 228, with power taken 
from an alternating current line, and stepped-up 
through a small transformer, gives much stronger trans- 
mission than is possible with batteries and a coil. 
The spark gap is connected across the secondary of the 
transformer, just as in a simple set. In series with 



260 



BOYS' BOOK OF ELECTRICITY 




WIRELESS TELEGRAPHY 261 

coil and spark gap is a condenser and one side of the 
oscillation transformer. The other side is connected 
between the aerial and ground. For best results the 
clips C and D are moved until the strongest waves are 
secured. 

For a tuned receiving station it is necessary to add an 
ordinary fixed condenser, a variable condenser, and a 
double slide tuner to the simple circuit shown. The 
fixed condenser is made of thin metal plates separated 
by insulating material or by air. The variable con- 
denser must have a movable set of plates which can be 
moved in and out between the opposite plates, giving 
whatever capacity is needed. The tuner is simply a coil 
of wire arranged with two sliding contacts, so that any 
part of the coil desired may be included in the circuit. 
Proper adjustment of the tuner slides and the variable 
condenser enables you to hear plainly messages which 
could not be detected at all without the tuner. Like 
the transmitting apparatus, the receiving circuit may 
either be close coupled or loose coupled. 

MAKING WIRELESS APPARATUS — THE AERIAL 

Every wireless station needs an aerial, or set of wires 
strung at a height above the station. They are doubly 
important, since they are used both for sending and 
receiving messages. It is quite necessary that they be 
clear of surrounding trees and buildings. By noting 
what a few other boys in your neighborhood are using 



262 



BOYS' BOOK OF ELECTRICITY 



you will see that there are several styles. This naturally 
raises a question as to which is the best for your use. 

It cannot be said that any one is best in all cases. 
The kind to put up depends entirely on conditions. A 
few of the most popular kinds are illustrated in Fig. 



loop Aerial 




T. Aerial 
Fig. 229. — Types of aerials. 

229, and each one has its special advantages. If only 
one support is available, either the loop or the inclined 
type should be used. For all-round work where two 
supports are to be had the "T" type is generally pre- 
ferred. Under the same conditions some prefer the 
inverted "L" type. 



WIRELESS TELEGRAPHY 263 

As to the materials for aerial conductors; most ama- 
teurs prefer bare copper wire. In size this should not 
be smaller than No. 14 B. & S. gage. Aluminum wire 
can also be used and has the special advantage of very 
light weight combined with great strength. Iron wire 
is not good for the purpose as it greatly decreases the 
sensitiveness of the set. 




Fig. 230. — Atrial spreader. 

In picking a site for the aerial and buying wire it is 
well to provide for a span of at least 50 feet. Even 
longer is preferable. The location is governed entirely 
by circumstances. Two convenient roofs are often 
used. Some boys string the wires in an attic. Where 



Fig. 231. — Aenal strain insulator. 

room can be spared in a back yard or vacant lot it is a 
good plan to set up two strong wooden or iron masts 
properly stayed. Iron is about as cheap and much 
easier to handle than wood, since the different sizes can 
be screwed together with reducers to make a pole any 
length and size you want. 



264 BOYS' BOOK OF ELECTRICITY 

At each end of the aerial wires there must be a wooden 
"spreader." These spreaders can be made of wood 
ij inch thick, each piece being cut 3 -to 4 feet long. 
Near each end of the spreaders put in a heavy screw- 
eye. Opposite to these and spaced equally put in four 
slightly lighter. The two heavy screw-eyes receive the 
supporting ropes; the lighter ones support the aerial 
wires. Strain insulators can be attached either to the 
ropes that hold the spreaders or between the spreaders 
and the aerial wires. The latter is usually preferred. 
In this case eight strain insulators will be needed. 
They can be bought at a cost of from fifteen cents up. 




Fig. 232. — "Golf -ball" strain insulator. 

If you like you can make very good insulators from old 
golf balls. In using these the first thing to do is to 
clean all the paint off, since it is a fairly good conductor. 
Next screw in two short heavy screw-eyes opposite each 
other. Care must be taken that they do not meet in 
the middle. Then wire or heavy cord can be passed 
through the screw-eyes to fasten the balls together. 
An insulator of this kind is shown in Fig. 232. 

Assuming that the aerial is to be of the "T" type, 
the conductor which goes to the detector and spark 
gap will be fastened across the middle of all three wires. 
There are several ways of making the connector, which 



WIRELESS TELEGRAPHY 265 

is called a "rat-tail." A very good scheme is to saw 
out a triangular piece of board \ inch thick and attach 
five good-sized binding-posts to it. Such an arrange- 
ment is illustrated in Fig. 233. The four top posts go 
to the wires of the aerial, and the bottom one to the 
transmitting and receiving station. All five posts 
should be connected with copper strips, which should be 
screwed tightly under the posts. 

Having attached the rat-tail to the wires and the 
strain insulators and rope to the spars, they can be 




To Insfrumenti 

Fig. 233. — An efficient rat- tail. 

raised and the aerial stretched. No matter what type 
of aerial is used, pulleys should be provided for raising 
it in place. Do not make the mistake some boys do 
of tying the aerial fast to the poles and then raising 
them, as it may be necessary at any time to let down 
the wires for repairs. A "kink" which will save time 
and temper is to put a large screw-eye bolt below each 
pulley. This will guide the rope and keep it from 
jumping out of place and catching while the wires are 
being raised or lowered. 



266 BOYS' BOOK OF ELECTRICITY 

The aerial conductors should always be kept quite 
taut and stretched evenly. The leading-in wire which 
extends from the rat-tail to the spark gap should be 
well insulated and should pass through a heavy por- 
celain tube where it enters the house or workshop. 
Of course, such insulators can be bought, but you can 
make a very good one with little trouble or expense. 
First secure a fibre tube at least an inch in diameter 
and 6 inches long. Then get a brass or copper rod 
4 inches longer and fasten a binding-post on each end. 



JBras J Rod \ ss ^^^^ E§HI ^ ' PoS 1 




Binding / 
Fig. 234.— This lead-in is substantial and easily made. 

Around this rod wrap paraffined paper until you can 
just squeeze the roll in the tube. Then heat the whole 
thing; add a little more paraffin if necessary, and the 
insulator is complete. For convenience it can be 
mounted on a board as shown in Fig. 234. One bind- 
ing-post then is connected to the aerial outside the 
house, and the other to the set in the house. 

As to the location for your transmitting and receiv- 
ing apparatus; it will be hard to find a better place 
than a good dry basement. Here a fine ground on the 
water pipe is nearly always handy, you are out of the 



WIRELESS TELEGRAPHY 267 

way, and you can have your workshop handy. A good 
ground connection on a convenient pipe may be made 
as illustrated on page 220. 

HOW TO FIGURE THE NATURAL WAVE LENGTH OF YOUR 

AERIAL 

The waves sent out and received to advantage by 
the aerial you put up will depend to some extent on the 
length of the wires and their height from the ground. 
Every aerial has naturally a particular length of wave. 
This is called its " natural" wave length. In a simple 
system it is very nearly four and one-half times the 
length of the aerial plus the distance to the ground. 
With tuners and condensers the natural wave length be- 
comes longer — it is then nearly 4.7 times the sum of 
the two lengths given. 

As an example, suppose that your aerial is 50 feet 
long and raised 40 feet in the air. The natural wave 
length would then be 

(50 + 40) X 4.7 = 90 X 4.7 = 423 feet. 

To change feet into meters divide by 3.28. 

423 -I- 3.28 = 128.9 or > practically, 129 meters. 

This is for figuring an inverted a L " aerial or an inclined 
aerial, where the rat-tail is at the end of the wires. In 
a "T" aerial, with the rat-tail in the center, add in only 
half the length of the stretched wires. 
The natural wave length of any type is made con- 



268 



BOYS' BOOK OF ELECTRICITY 



siderably longer in the tuning process by use of the 
double slide tuner or loose coupler in receiving, and the 
helix or oscillation transformer in transmitting. It 
will be well to remember that the wave length cannot 
be increased very much in sending. Present United 
States wireless laws are quite strict, and will not allow 




sort 




Fig. 235.— Measuring "inverted L" and "T" aerials for natural wave length. 

you to send waves over 200 meters long, although you 
can, of course, receive waves practically any length. 



A SIMPLE DETECTOR 

The first piece of wireless apparatus made should be 
your detector. The fact that it is so simple makes it a 
good piece to start on. The main things needed are a 



WIRELESS TELEGRAPHY 269 

short piece of J-inch brass tubing, a piece of galena, two 
binding-posts, and a rubber knob of the sort used on a 
typewriter carriage. In the knob fix a piece of brass 
wire about 1 inch long and small enough to pass 
through a hole in the binding-post. Mount this post 
at the edge of a board base 2 \ inches square. Break 
a chip of galena off and fit it in the little brass tube. 
Then fasten the tube upright at the opposite edge of 
the base. A piece of wire should be soldered to the 




Fig. 236. — "Cat whisker" detector. 

tube and brought to a second binding-post for con- 
venience as shown in Fig. 236. 

The "cat whisker" that gives this detector its name 
should now be fixed. As the word indicates, the wire 
of a " cat whisker " is very fine. It should be phosphor- 
bronze either No. 30 or No. 32. Solder one end of it 
with a small drop of solder to the end of the brass rod. 
Then bend the other end until it strikes about the mid- 
dle of the crystal of galena. The pressure of this wire 
on the crystal can now be regulated by turning the 
rubber knob. When the best point is reached the 



270 BOYS' BOOK OF ELECTRICITY 

adjustment is held by tightening the little brass screw 
in the top of the post. 

The important thing in the detector is to have a very 
delicate contact. This may be secured in a number of 
ways with many different materials. A detector from 
which good results may be had can even be built from 
two safety razor blades with a piece of lead from a 
pencil, or, better still, several pieces of carbon filament 




from an incandescent lamp stretched between them. 
This is a simple form of the microphone which has 
already been described. 

A very common and substantial detector may be 
made by bending a piece of strap brass in the shape 
illustrated by Fig. 237, and mounting this with a suit- 
able screw adjustor and a piece of fused silicon. Here 
the fine wire is coiled in a delicate little spring. The 
regulation is very close; also the tip of the wire strikes 



WIRELESS TELEGRAPHY 



271 



points all over the top of the mineral, so that the most 
sensitive point can be picked out. In making this 
detector the brass cup should be filled with melted 



Solder 




5iUcor) 



Fig. 238. — Cup of silicon detector. 

solder, and a thin piece of silicon ground flat and pressed 
down in the hot solder. The appearance of both parts 
finished up are shown in Fig. 238. 



DOUBLE-SLIDE TUNER 

When you add a double-slide tuner to your aerial, 
detector, and telephone receiver you have all the 
apparatus that is absolutely necessary for receiving 
messages. The tuner not only increases the loudness 
of the signals, but allows you to get rid of some dis- 
turbances from waves you do not want to hear. 

To make this tuner, first secure two brass rods each 
\ inch square and 8 inches long. Through both ends 



272 



BOYS' BOOK OF ELECTRICITY 



of each should be bored a yV -inch hole for a wood screw. 
About 200 feet of No. 22 enamel-covered wire will also 
be needed for the winding. 




From a piece of bristol board or several layers of 
heavy paper coated with good glue roll a tube 3 inches 



WIRELESS TELEGRAPHY 



273 



in diameter and 7 inches long. This should be made 
quite stiff. When the glue is dry, paint it with two 
coats of shellac, letting it dry thoroughly; then bake 
it for several hours in a fairly warm oven. This will 
prevent shrinking and loose coils later. Now wind the 
wire on evenly and smoothly, fastening each end by 





Fig. 240. — Ends for tuner. 



passing it several times through the cardboard center. 
It is well to shellac the finished winding once more. 

Winding and bars can now be mounted on a base. 
For this part cut a board 5 by 9 inches. Cut two 
ends each 4 by 4 inches. Trim off the corners and 

mortise to hold the slider bars. Two additional cir- 

18 



274 



BOYS' BOOK OF ELECTRICITY 



cular pieces will be needed for attaching the cylinder. 
These must just fit inside the tube and are to be screwed 
inside the end pieces. The tube can be fastened in 
place later with small tacks. Only one fixed connec- 
tion with the wire is made. One of the ends of the 
wire coil should be attached to a binding-post set in 
the middle of one end piece. The two other binding- 
posts may be placed on either end piece near the mor- 
tises which are to hold the bars. 



5> 




Fig. 241. — A slider that is easy to make. 



For the two sliders a piece of square tubing that will 
just fit nicely over the J-inch rod will be needed. A 
piece 3 inches long will make both sliders. The com- 
mon trouble of fitting handles is avoided if the scheme 
indicated in Fig. 241 is followed out. Any little wooden 
or rubber handle can then be used and easily screwed 
or riveted in place without interfering with the smooth 
movement of the slider. 

Before screwing the bars in place note where the 



WIRELESS TELEGRAPHY 275 

sliding contact will touch the wire. Then along these 
two lines scrape clear paths in the insulation. Be very 
careful not to cut or dent the wire or to take away the 
insulation from between the turns. 

With the bars in place one of the binding-posts should 
be connected to each by a stout piece of wire or copper 
strip. This completes the instrument. For finish, two 
coats of shellac should be applied to the wood work. 

A LOOSE COUPLER THAT YOU CAN BUILD 

If you have been receiving with a double-slide tuner 
in the circuit, you will be surprised to see how much 
better results a loose coupler like the one in Fig. 242 
will give you. For this eight pieces of wood cut to size 
will be needed. The dimensions of the base are indi- 
cated in the drawing. Instead of one stiff paper or 
bristol-board cylinder two will be needed. One of these 
should be 4 inches long and 2 J inches in diameter; the 
other 3! inches long and 2 inches in diameter. The 
larger tube should be fixed in place between the two 
end pieces. To do this fit one end with a disc of thin 
wood and tack the cardboard to it. Then fasten the 
wood with screws to the thicker end piece. For the 
other end cut a circular hole in the second end piece 
and fit the cardboard tube inside it. Gluing this end 
is easier than tacking and answers as well. Now wind 
the tube from end to end with a layer of No. 22 single 
silk-covered or enameled wire. One end of this at- 



276 BOYS' BOOK OF ELECTRICITY 



WnH 



I 






ill 



1 




taches to one binding-post. The outer end is simply 
fastened by passing it through pinholes in the card- 



WIRELESS TELEGRAPHY 277 

board. The remaining post is, of course, attached to the 
end of the single-slide bar. For the secondary No. 26 
wire will be needed. Before winding this on, it will be 
necessary to fix the five switch points in the round 
wooden piece that makes the head. Five of the points 
will be needed. They can be made from flat-headed 
brass machine screws. The switch can be made from 
a flat strip of brass and provided with a hard wood or 
rubber handle. The inside connections for this sliding 
secondary are shown plainly in Fig. 242. After the 
coil is finished and the connections made, a round 
wooden piece must be inserted in the other end of the 
tube to act as a guide. Two holes in this piece and 
the piece holding the five-point switch permit the 
brass rods to pass through so that the coil is easily slid 
in and out of the larger fixed coil without touching any- 
where. A piece of lamp cord connected to the two sec- 
ondary binding-posts and passing through a hole in the 
wooden coil head connects to the switch and one end 
of the coil. 

In using this tuner the number of turns in the primary 
is regulated by working the little brass slider. Current 
in these turns induces current in the turns of the 
smaller secondary. The secondary can be slid in and out, 
and the number of turns changed with the five-point 
switch. Very fine regulation is possible, as the switch 
and the double slide arrangement allows you to change 
the inductance to practically any value. 



278 



BOYS' BOOK OF ELECTRICITY, 





[\. 








h 


V 


\h 


^7 


IT 


1 




* 


42 s. 




In 


X 


N 


1 


n. 








FIXED CONDENSER FOR RECEIVING 

You can build a good condenser for this purpose 
from paraffined paper and tin-foil sheets. Twenty 



WIRELESS TELEGRAPHY 279 

sheets of paper will be needed, each cut to 4 by 5J 
inches. Nineteen sheets of tin-foil each 2§ by 3 inches 
make up the metal part. Between each tin-foil sheet 
is a sheet of waxed paper, and half of the tin-foil leaves 
stick out a distance of J inch at each end. For top and 
bottom cover secure two pieces of hard rubber, wood, 
or fibre board 4 by 5^ inches. Bore a |-inch hole 
near each corner. These are for connectors and also 
to hold the condenser together. Two connecting strips 
should be cut from thin sheet brass or copper. They 
should be bent over the tin-foil ears and held under 
the connecting screws. Small binding-posts, such as 
are used on dry batteries, will answer for connections 
and for holding the plates together. The connecting 
strips are clamped under the washers at two corners, 
making firm connections with the sets of tin-foil sheets. 
When the condenser is mounted tie a piece of tape 
around the edge. Cut one hole for pouring and an- 
other to let the air out, and fill with melted paraffin. 
About the same result is secured if the sheets are rolled 
instead of being laid flat and the whole thing bound 
with rubber bands and inserted in a fibre tube. Wooden 
plugs at each end close the tube tightly and also allow 
the binding-posts to be fastened on. 

VARIABLE CONDENSER 

This is not an absolute necessity and is omitted from 
many good receiving sets. Still it is not hard to make 



280 



BOYS' BOOK OF ELECTRICITY 



and will sometimes help considerably in getting satis- 
factory tuning. It can be made from six ordinary 
5 by 7 inch photographic plates and two sets of metal 



1. 



Fig. 244. — Glass plate for condenser. 

plates, all held in a plainly made wood frame. The 
first thing to do is to clean the plates well and fasten 
them all together with little wood spacers between. 
These spacers may be held in place by a good china 




Wood, or 
Robber 
Strips 

Fig. 245. — Glass plates assembled 
with separating strips between. 




Brass or 
Aluminum Plate* 



Fig. 246. — Set of metal plates. 



cement. Half of them should be very thin, and the 
other half of the number a little thicker, as shown in 
Fig. 245, but all should be the same length and width. 



WIRELESS TELEGRAPHY 



281 



The stationary plates will then be held in the narrow 
spaces, and the sliding plates in the wider ones. If 
both plates are to slide, all the spacers can be made 
exactly alike. 

The next thing is to make up two sets of plates from 
thin brass or aluminum, each plate being cut to about 



33 



3S 



35 



x* 



Hard Rubber 

Knob 



Fig. 247. — How plates are assembled. 

3 by 7 inches so that it will slide in between a pair of 
the glass plates. For this condenser nine plates should 
be cut, all alike. Four-plates go to make up the sliding 
set and five to make up the stationary set or vice versa. 
The plates in a set should be held together at two corners 
only by long 'threaded bolts, with each plate gripped 
between two nuts. This scheme of fastening is indi- 



282 BOYS' BOOK OF ELECTRICITY 

cated in Fig. 247. The frame is built plainly as shown 
in Fig. 248. 

The metal plates are slipped in place between the 
glass separators from the two ends. A sheet of glass 
is now between each plate of one set and the nearest 




stationary 
Plates 



\ Sliding 
Plates* 



Fig. 248. — Variable condenser. 

plate of the other set. By sliding the movable set of 
plates in and out by means of a rubber handle which can 
be easily attached you have practically any capacity 
you need for tuning. 



TELEPHONE HEAD SET 

The sensitive receivers needed can hardly be made 
by the amateur. They can be purchased one at a 
time and later connected together, or the whole set 
can be bought complete. While the 75-ohm sets are a 
good deal cheaper than the 1000-ohm receivers, they 
are not by any means as delicate. The greater sensi- 



WIRELESS TELEGRAPHY 



283 




Fig. 249. — Wireless head set. 

tiveness of the higher resistance is worth a good deal 
in increased clearness of signals. 



INSTRUMENTS FOR TRANSMITTING — INDUCTION-COIL 

The thin spark of the ordinary induction-coil does 
not give as good a range as those made especially for 
the purpose. The spark of these special wireless coils 
is much "fatter." Heavier wire is generally used in 
the winding of the secondary coil. 

One authority gives this general rule for building 
wireless spark coils: Use ij pound of No. 32 wire on 
the secondary for each inch of spark up to 6 inches; 
then allow 2 pounds to the inch. For the primary use 
two layers of wire according to the following table : 



284 BOYS' BOOK OF ELECTRICITY 





TABLE FOR 


INDUCTION-COILS 


Core diameter. 


Core length. 


Spark length. 


Primary wire. 


(Inches.) 


(Inches.) 


(Inches.) 




h 


6 


I to I 


No. 16 


I 


8 


I tO 2 


No. is 


* 


9 


2 to 4 


No. 14 


i 


IO 


4 to 8 


No. 13 


il 


12 


8 to 12 


No. 12 



While it is really an economy to buy a good wireless 
coil if one is to be used, this table is given for boys who 
want to try their hand in making up their own. 

TRANSMITTING KEY 

The ordinary telegraph key does very well with a 
small set. When you send to your chum four or five 
miles or even further away you will need something 
better able to stand sparking. Special wireless keys are 



Fig. 250. — Sending key for heavy current. 

made, but you can easily build a serviceable one your- 
self. Take a strip of spring brass like the one shown 
in Fig. 250 and solder a wide U-shaped piece of 
copper or brass wire to one end. Drill four holes in 
the strip; two at one end, for the screws that hold it to 



WIRELESS TELEGRAPHY 285 

the base; one at the other for the knob, and the fourth 
about in the middle for a screw which limits the up- 
stroke of the key. A bit of f -inch hard wood 3 by 4 
inches will answer for the base. Before finally putting 
the spring in place find exactly where the wire tips will 
come when the spring is down. Bore a J-inch hole 
about half-way through the base at each of these points. 
Run a copper wire from a single binding-post to both 
of the holes. Connect the second post to the base of 
the spring. Place a drop of mercury in each hole and 
the key is complete. Contact between the mercury 
and wire is always good, and the mercury is easily 
renewed. 

THE HELIX 

Here is the simplest device for tuning a transmitting 
set. It consists of a heavy copper or aluminum wire 
wound on a four-post wooden frame, as shown in 
Fig. 226. One end is brought up to a binding-post; 
the other is simply made fast to the frame. The bind- 
ing-post can then be connected to the aerial. The 
other connection is made by means of a metal clip 
which can be fastened to the coil at any point. This 
coil puts inductance in the circuit and increases the 
wave length. When sending, the helix clip is adjusted 
until the best radiation is secured. Ordinarily this 
point is found with a little instrument called the "hot- 
wire ammeter. ' ' Sometimes good results can be secured 
with a little incandescent lamp connected in series with 



286 



BOYS' BOOK OF ELECTRICITY 



the aerial. When the lamp burns brightest the radia- 
tion is most powerful. 

A somewhat more compact helix than the kind 
described above can be made by winding a coil of 
copper strip in a flat frame. Such a frame can be made 




Fig. 251. — Helix for tuning transmitting set. 

from two J-inch boards each 14 inches long. These 
serve both as a base and a support for the coil. The 
metal ribbon is held in slots cut with a fine saw. In 
cutting these begin 2 inches from the center and space 
the cuts J inch apart. About 50 feet of the strip will 



WIRELESS TELEGRAPHY 



287 



be needed. Put one end of it in a slot nearest the 
center and wind out, keeping the turns well rounded. 
A helix with crooked bends makes a poor looking job. 
As you go along pound each turn down into the slots 




Fig. 252. — Oscillation transformer for closer tuning. 

with a wooden mallet. At the end of one of the arms 
of the base set in a binding-post. Solder a connecting 
strip to it and the end of the helix. It is ready to work, 
but you can make a really fine looking job of it by 
painting the woodwork over with a coat of lampblack 



288 BOYS' BOOK OF ELECTRICITY 

and then shellacking and polishing it. This will give a 
finish like hard rubber. 

Still better timing is possible with an oscillation 
transformer. This is simply two helix coils that can 
be set at any distance from one another. The brass 
rod which supports the upper coil should be a fairly 
tight fit in it. Then the coil will slide back and forth, 
but will stay where you put it. 






Fig. 253. — Easily made helix clips. 

Helix clips for connecting the aerial and spark-gap 
leads to the coil are easily made. A brass strip can 
be bent to grip the metal strip tightly, or a spring 
clothes-pin can be fitted with a copper grip and a 
binding-post for connection. A few forms of clip are 
illustrated in Fig. 253. 

A GLASS PLATE CONDENSER 

A good condenser makes a wonderful difference in 
the quality of your work. One can be made from a few 



WIRELESS TELEGRAPHY 



289 










^ 












71 

3>© 












\ts 






19 



290 



BOYS' BOOK OF ELECTRICITY 



photographic plates and some tin-foil that will answer 
all purposes. Old plates can be secured from any 
photographer. Clean the gelatin off thoroughly. Then 
shellac one side of all four plates and carefully put a 
square of tin-foil 2 by 4 inches exactly in the center of 
each. Let it dry in place. When thoroughly hard, put 
tin-foil squares on the opposite side in the same way. 

Now build a frame as open as possible, but substan- 
tial. Fix two slotted pieces in the bottom to hold the 
plates an inch apart, and a third one to space them at 



Brass Rod 




^•Brass Strip 



Fig. 255. — Test-tube condenser. 



the top. Both of these should be well paraffined. 
On the cross-pieces at the ends fix the two binding- 
posts. Brass strips bent to shape and held under these 
make the contact with the tin-foil. The post at one 
end should connect with the inside foil of the two 
middle plates and the outside of the two outer ones. 
The other post then connects with the inside of the 
outer plates and the outside of the middle ones. More 
plates or less can be used according to the character of 
aerial and spark. 



WIRELESS TELEGRAPHY 



291 



Another form of condenser may be made from test- 
tubes. One of this sort is shown in Fig. 255. 

The transformer is a little beyond the scope of the 
amateur. It is better to buy a standard make of wire- 




Fig. 256. — Transformer used for wireless. 

less transformer if one is to be used. Such a trans- 
former is shown in Fig. 256. 



SPARK-GAP 

After a little experience with good and bad spark-gaps 
you will find this little piece of apparatus quite impor- 
tant. For one of the simplest types, and one that gives 
good results, zinc rods are used. A zinc spark-gap is 
quite easy to make. All that is needed is two zinc 
rods and two large brass binding-posts in which the 
rods can be clamped firmly. If desired, sealing-wax 
handles can be added. When the posts are solidly 
mounted on a little wooden base the gap is ready for 
use. The length of spark can be easily adjusted so that 
it gives best results. 



292 



BOYS' BOOK OF ELECTRICITY 



When you connect your set, try to see how neatly 
and not how quickly you can place the different pieces 



Zinc Rods 




Fig. 257. — Zinc spark-gap. 

of apparatus. Here are a few tips for connecting the 
transmitting set. Use copper strips for connections 




Fig. 258. — Vertical spark-gap. 



instead of bell wire; run the conductors parallel and 
as far apart as possible; make all joints at right angles 
and solder every joint carefully. 



WIRELESS TELEGRAPHY 293 

Every boy who is going to put in a set should first 
find out about the "Radio" club in his neighborhood. 
Pointers from other boys with a little experience often 
saves trouble and embarrassment later. The United 
States Radio inspectors are quite particular about 
badly tuned waves, especially as they approach the 
200-meter limit. In order that all amateurs may enjoy 
the use of their sets it is necessary that each one should 
avoid disturbance, fake distress calls, and so on. 

THE BUZZER TEST 

The buzzer test is not hard to arrange, and it gives 
you a sure indication that your detector is properly 
adjusted. All the additional material that you need is 
a dry cell or two, a small buzzer, and the necessary wire. 
The buzzer has to be wired in so that it works when 
you press a key or push-button. Of course, you could 
send messages to yourself with this buzzer arrange- 
ment just as you could with a Morse key and sounder, 
except that the clicks would be replaced by buzzes. 
With the test the point is to fix the buzzer so that you 
cannot hear it except through the telephone receiver. 
This can be done either by putting the buzzer away in 
some other room, or by mounting it in a little box with 
cotton wrapped around it. 

The buzzer is connected in according to Fig. 259. 
Two or three loops in the buzzer circuit wire go inside 
a single loop in the ground wire of the receiving set. 



2Q4 



BOYS' BOOK OF ELECTRICITY 



The detector is connected as usual. For the test you 
simply send signals with the buzzer button or key and 
listen through the telephone receiver. The oscilla- 
tions started by the buzzer induce slight currents in the 



To Aerial 



P*-*f 



Butter 



nr^** 



d 




Ground 
Fig. 259. — Buzzer connected to test detector adjustment. 



aerial circuit. When the signals are heard plainly 
you may know that your detector is properly ad- 
justed. 

When good results are secured you are ready to 
receive. For this the next step is to set the loose 
coupler or double-slide tuner to a point where some 



WIRELESS TELEGRAPHY 295 



INTERNATIONAL MORSE CODE 

1. A dash is equal to three dots. 

2. The space between parts of the same letter is equal to one dot. 

3. The space between two letters is equal to three dots. 

4. The space between two words is equal to five dots. 



B _ . • . T — 

I! • •- 



D — .. V "» 



C — . — . 

W 
X 
Y 



F. . _ - — • 



H . . • ♦ Z 



G — 1 — • 



I.. 1 •_ — __ 

L • MB • • 4 • • • • MB 

M _ _ 5 • • • • • 

N mm • 6bb«« ## 

R • — • 0___.„. 

Fig. 260. — International Morse code. 

message is heard plainly. Then finer adjustment is 
secured by regulating the variable condenser. 

A FEW WIRELESS STUNTS 

Although the common method of receiving wireless 
messages is with the telephone head-set, another 
method is possible. For this a device called the 



296 



BOYS' BOOK OF ELECTRICITY 



"coherer" is needed. It is used with a relay and an 
ordinary telegraph sounder. Both are described in 
Chapter X. 

The coherer was the first instrument to receive 
messages. It is so simple that you can easily make one. 

■ Glass Tube 

■Nickle Filin&s 




Fig. 261. — Coherer. 

All there is to it is a pinch of nickel filings and a much 
smaller amount of silver filings. These are enclosed in 
a tube of glass or any good insulating material. The 
little pile of filings is held in the tube between two 
brass rods which fit the tube quite closely. 




Fig. 262. — Coherer and tapper. 

Filings in such a loose heap hardly conduct electricity 
at all under ordinary conditions. Just as soon as an 
electromagnetic wave comes along through the ether 



WIRELESS TELEGRAPHY 



297 




there is a big difference. The filings at once become 
good conductors. If they fell apart again for the next 
wave the coherer would be very simple; but they do not 
act that way. After the wave passes they continue to 



298 BOYS' BOOK OF ELECTRICITY 

stick together. An actual shock is needed to separate 
them. The little knock of an electric bell tapper does 
the business in good shape. The gong is removed and 
the bell connected so that there is a tap every time the 
filings cohere. The action is this: a wave passing 
allows a little current to work the relay; then the tele- 
graph sounder is operated by the heavier local current. 
The same current works the tapper, so that the filings 
are jarred. With this arrangement you get about the 
same clicks as in an ordinary metallic telegraph circuit. 
There are a lot of things you can do with a coherer. 
You can fire off a charge of flashlight powder in another 
room, ring a bell, light a lamp, or arrange connections 
for other stunts. A lot of ingenuity can be exercised 
in arranging electromagnets, switches, and batteries 
to do whatever you like by wireless control. 



CHAPTER XIII 

House Wiring 

There is as much room for a display of skill in wiring 
a house for electric light as there is in building and 
operating a wireless set or a telephone line. Of course, 
wired houses are so common these days that few of us 
stop to think about how the wires were put in or just 
where they he back of the wall. As simple as the wiring 
of a small house may look to you, it is likely that con- 
siderable thought was given to the wiring so that lights 
and switches would be just where they were wanted and 
the wire put in with the least possible material and 
labor. Any house that is to be wired deserves this 
consideration. Outlets for fixtures, floor lamps, flat- 
irons, and so on should be planned very carefully. 
Much credit is due to the boy who can not only plan 
the wiring of a house, but can also make a good job of 
running the wires. 

After all it is not so hard to bring current from the 
electric line to your house if you plan and study the 
work carefully. Neither is it beyond a boy handy with 
tools to distribute the current so that it can be avail- 
able where needed and safely controlled. If you live 

299 



300 BOYS' BOOK OF ELECTRICITY 

in the city you may not be allowed to do the work, but 
you can plan it anyway and see how your ideas work 




t.ain Switch 



\ Porce1oir\ 
Knobs 

Fig. 264.— Room wired with molding. Floor broken away to show service 

switch. 

out. If your home is in the country there is nothing 
to keep you from doing all the work yourself. 



HOUSE WIRING 301 

If you take the work into your own hands, there are 
two schemes for you to choose from. The first and 
easiest is to run the wiring in wooden molding along 
walls and ceilings, using porcelain tubes to carry 
wires through walls and floors. The other is to run the 
wiring between the ceiling and the floor above, carrying 
it back of the plaster on the walls. In this way you can 
do a better, more professional looking job than is pos- 
sible with the wooden molding. 

WIRING IN MOLDING 

The wood molding used for this work is made in long 
flat strips of wood, each with a double groove running 
the full length. These strips fasten with long nails 
right to ceiling or wall. The wires are laid after the 
strips are in place and held in by a thin strip which acts 
as a cover. Particular attention must be given to 
getting molding on perfectly square and straight, as 
carelessness always shows up very plainly in a molding 
job. 

Before starting on any wiring job it is well to find out 
just how much wire you are going to need and how much 
molding. To do this it is well to draw up a little plan 
of the house, and decide just where the circuits are to 
be run and the lights located. As an example, take a 
five-room cottage with two bedrooms, sitting-room, 
dining-room, and kitchen. There will be at least six 
outlets; that is, one for each room and one for the hall. 

\ 



302 



BOYS' BOOK OF ELECTRICITY 



By " outlet " is meant the place where the current is 
brought out for use, whether it is to lamps, washing-i 
machine, flat-iron, or anything else. All of the outlets 
in Fig. 265 are for lamps. The position of each one is 
indicated by a cross. After all outlets have been 
decided on, figure carefully all the runs of wire, up 




Fig. 265. — Plan of house with molding indicated by lines, and outlets by- 
crosses. 



walls, across ceilings, through floors, and so on; then 
add about 20 per cent, to your estimate. 

Almost any kind of fixtures may be used with this 
style of wiring, but the ordinary drop light is by far 
the commonest. With the drop light a wood or por- 
celain rosette is usually fastened to the ceiling or on the 
molding where light is wanted, and the lamp simply 
hung by a flexible cord. Especial care must be taken 



HOUSE WIRING 



303 



where branch circuits are run, and all joints must be 
well soldered and taped. Switches can be put in where 
wanted and wired according to the scheme indicated 
in Fig. 273. 

For running the circuits rubber-covered wire at least 
as large as No. 12 B. & S. gage should be used. All of 






Fig. 266. — Service switch. 

the circuits in the house must in some way be con- 
nected in multiple with the wires which run to the 
service box in the basement. This box can either be 
bought or made. It is simply a fire-proof case con- 
taining a double pole switch and fuses. If home-made 
it can be built by lining a good wooden box with asbes- 
tos. Such an arrangement is indicated in Fig. 266. 



304 



BOYS , BOOK OF ELECTRICITY 



Remember these two points before you wire up your 
service box: first the wires from the power line should 
come to the fuses and not to the switch itself; second, 
the switch should be placed so that the handle is pulled 
down to open it. This is done to prevent the switch 
from accidentally " falling " shut. The two fuses simply 
protect the circuit. If too heavy a current flows for 




Fig. 267. — How cleats are attached to rafters in wiring barn. 

any reason they will burn out instead of melting the 
wires. 

Porcelain cleats provide even a simpler method of 
wiring, but are only'used for barns, workshops, and so 
on. With this style of wiring practically the entire 
circuit is in view at all times, so that a fault can be very 
easily discovered. 



CONCEALED KNOB AND TUBE WORK 

A few boards will have to be taken up if you do con- 
cealed knob and tube wiring, but the workmanlike 



HOUSE WIRING 



305 



result that is secured more than pays for the extra 
trouble. For wiring the first floor a little sawing and 
cutting will have to be done on the floor boards of the 
second story. Parts of the baseboard will also need to 
be taken out. Wires for the second story can usually 
be put in the attic with very little work. 

As the wires in knob and tube work run in the space 
between ceiling and floor they have to be carried along 
the floor joists on knobs, or passed through them in 
porcelain insulating tubes. In Fig. 268 a run of wires 




Fig. 268. — Knob work with pockets cut. 

on knobs is illustrated, and in Fig. 269 the method is 
shown of carrying them in tubes. The knobs are usu- 
ally held in place by wire nails. The tubes are simply 
forced into the holes that are drilled in the joists to 
receive them. 

After the wiring has been planned in a general way 
the first step in running knob and tube work is to mark 
the plaster or wall-paper of each room for outlets and 
switches. Be careful to get the lighting outlets ex- 
actly in the middle of the room, or spaced evenly from 



3°6 



BOYS' BOOK OF ELECTRICITY 



the sides if there is to be more than one drop light or 
chandelier. After the outlet mark is made on the 
ceiling, bore from below with a long thin bit clear up 
through the floor of the room above. This will indi- 
cate where the first pocket is to be cut. By "pocket" 
is meant the cutting of a board to allow knobs to be put 
in place and the wires fished through. If the wires 
run along between two rafters it will not be necessary 
to take whole boards up, but only to cut a number of 




Fig. 269. — Floor removed to show tube wiring. 

such pockets about 4J feet apart along the line. These 
pockets are illustrated in Fig. 268. In making them 
the floor boards should be sawed just as close to the 
rafters as possible. The position of the rafter should 
first be located as closely as possible by tapping on the 
floor. Then by boring a small hole and feeling with a 
piece of wire you can with a little practice tell exactly 
where the joint is. Use a thin keyhole saw for making 
the cuts. Nail the knobs about 2 inches below the floor. 



HOUSE WIRING 307 

When running tubes, holes should be bored through 
each rafter about 4 inches apart and just large enough 
to make a snug fit on the tube. Of course, each one 
will slant down a little, but the only effect of this 
will be to make the wire a little harder to pull. Some 
branches of the circuit will always have to run crosswise 
of the rafters in tubes, and along this path the whole 
board, or perhaps two, will need to be taken up, and 
each rafter bored in two places. 








Tube 

r 8 "n 



Knob 



Cltctt 
Fig. 270. — Insulators for knob and tube and cleat wiring. 

After all the knobs and tubes are in place you are 
ready to go ahead with the actual wiring. The best 
way to start this is to lay your two coils of insulated 
wire on the floor near the point where the wires will 
run down to the service box. Take an end from each 
coil and run the two ends under the floor from pocket 
to pocket and through the tubes until the end 
of the circuit is reached. If there is to be an outlet 
at this point leave a few inches extra to connect on 
later. 



3 o8 BOYS' BOOK OF ELECTRICITY 

Every one of the knobs must now be fastened onto 
the wire it is to carry. About the best way of doing this 
is with a hitch. To make the hitch simply tie a piece of 
insulated wire about 14 inches long around the knob and 
the main wire, twisting the ends around the wire as 
shown in Fig. 271. 

With all wires properly joined and tied to the insu- 
lators, the ends of the coils that remain should be cut to 
about the proper length to reach the service box. 
These ends should then be protected by pulling them 
through lengths of circular loom or "Flexduct." This 




Tie U/tne. -^ 

Fig. 271. — How to tie wire to knobs. 

supplies the extra insulation that is needed on account 
of lack of insulators. A weight can then be tied to the 
wires and the ends dropped down behind the plaster 
to the service box. 

In every job of wiring it is necessary to run branch 
circuits, which involves both splicing and soldering. 
All splices should be made very carefully, and the joints 
finished with good solder and a non-corrosive flux. 
This soldering should be done with a little blow torch 
or an alcohol lamp. Solder is most convenient in the 
form of solder " wire." While the joint is still hot from 



HOUSE WIRING 



309 



soldering it should be wrapped with rubber tape and 
then with friction tape. This makes the insulation 
practically the same as at the other points. Remember 
that neither the insulation nor the joint gets any better 
than it is right at first; it always gets worse as time 
goes on if not done thoroughly. When such a splice 
is made be careful that the two wires do not cross in 
such a way that the insulation may rub and cause a 
short circuit. It is always best to protect such a cross- 
ing with porcelain tubes strung along where necessary. 



Cleats to Hold 

Floor Board in 

. Place 




Ceil in 



«V\ 



X 



Fig. 272. — Ceiling plate in place at outlet. 

At each outlet for properly installing fixtures later 
a piece of board at least f -inch thick should be set in 
between the rafters just above the plaster. This will 
provide a firm hold for the screws that support the light- 
ing fixture. Care must be taken that the nails used to 
fasten this board in place do not slant downward too 
much and crack the plaster on the ceiling. 

All of the suggestions given are for wiring a small 
home. In buildings of this kind it is usually considered 
that one outlet for a chandelier or drop light in the 



3"> 



BOYS' BOOK OF ELECTRICITY 



middle of each room is sufficient. If desired, however, 
a reading lamp can be added in the library, and other 
lights for decorative purposes can be supplied from 
baseboard outlets. In the dining-room floor outlets 
can be placed conveniently so that the electric toaster, 
electric coffee percolator, or chafing dish can be used on 
the table. For the kitchen the electric iron is a great 




Fig. 273. — Connections for lamp and wall switch. 

convenience. This device should take current from a 
wall or baseboard outlet, and not from the drop light 
cord. In the laundry two extra outlets, one for a 
flat-iron and the other for the washing-machine, are 
great helps. 

In closets and pantry drop cords are generally used. 
Many fires are started by people who use matches in 



HOUSE WIRING 



3ii 



hunting for clothes, so you will be helping to make 
your home a great deal safer by adding electric lights 
in all the closets. 

SWITCHES 

In the library, dining room, and hall, at least, wall 
switches are quite a convenience. A snap switch or 




$ 




Fig. 274. — Lamp and wall switch installed. 

push-button switch will save a lot of fumbling in the 
dark, and perhaps upsetting furniture while hunting 
for the light. Each of these switches means an extra 



312 



BOYS' BOOK OF ELECTRICITY 



run of wire from the fixture down the wall to the switch 
terminals. The method of connection is shown in Figs. 
273 and 274. 

Three-way switches are a little more complicated, but 
are fine for a front hall. With one of these switches 




To 
Service 
Switch 

Fig. 275. — A light wired with two three-way switches can be turned on and 

off from either one. 



wired in at the top of the stairs and another at the bot- 
tom you can turn the hall light on and off from either 
of the two switches. The wiring used is shown in Fig. 
275. The switches are really wired in series, but are 



HOUSE WIRING 



3i3 



connected by two wires instead of one. When the light 
is off both of the wires are connected to the circuit, but 
there is not a complete circuit, since one wire is discon- 




Fig. 276. — How wires are brought into house. 

nected at one end and the other at the other end. Move 
either switch and one or the other of the wires is im- 
mediately disconnected, while the other completes the 
circuit and current flows through the lamp. 



3 i4 BOYS' BOOK OF ELECTRICITY 

SERVICE WIRES 

In bringing service wires from an electric line an iron 
conduit is generally used. This is attached to the side 
of the house as shown in Fig. 276. Insulators take the 




Fig. 277. — Wires brought through wall in porcelain insulating tube. 

strain from the pipe. A loop in each wire where it 
enters the top of the pipe gives the necessary "slack" 
and at the same time prevents the rain from following 



HOUSE WIRING 



3i5 



the wire down the tube and damaging the insulation. 
These loops in the wire are called "drip loops." Wires 
can also be brought in through porcelain insulating tube 
if this is preferred to using the conduit. 

WIRING LARGER HOUSES 

Nearly all of the wiring in cities is done either in 
flexible or rigid metal conduit. The flexible kind is 
generally used where old buildings are to be wired, as it 
can be quite easily run under floors and back of walls. 




F/ex/b/e 
Fig. 278. — Rigid and flexible conduit. 

The rigid style is put in when the wiring is done during 
construction of the building. The idea with both kinds 
is to furnish a complete metal path for the wires to 
run through. Then there is really nothing that can 
rub, crush, or damage the protecting insulation. 
Wherever branch circuits are to be brought out or 
switches are to be placed, iron "knock-out" boxes 
or outlet boxes are provided. The wire is then pulled 
through the conduit from one box to the next. With 
both flexible and rigid conduit special tools are required 



3 i6 BOYS' BOOK OF ELECTRICITY 

that put the work a little out of reach of the average 
amateur. 

Several uses of electricity and electric light are indi- 
cated in the full-page diagram, Fig. 279. For simplic- 
ity each of the circuits is shown by one wire instead 
of two. Note that here the service wires run first to the 
meter, and then divide into six separate circuits. 
Each circuit is provided with fuses, and the whole lot 
with a single large fuse placed in the main line. The 
panel shown is usually enclosed in a box of sheet steel. 
Briefly, the six circuits run as follows: 

To iron and washer in laundry. 

To floor outlet, chandelier, and ceiling lamp in dining- 
room, and to lamp in pantry. 

To baseboard outlet in dining-room. 

To chandelier in library, to fixture in attic billiard- 
room, and to sleeping porch. 

To lamps in parlor and bedroom. 

To baseboard outlets and porch lights. 

Of course, it would be possible to have all these lights 
on one circuit, but this is against the rules of the in- 
surance companies. By dividing the circuits the job is 
not only made more workmanlike and convenient, but 
is actually safer. Each circuit on any job should be 
planned so that it will never carry more than 660 watts. 
Eleven 60-watt lamps would, in other terms, be allowed 
to each. There are many other rules made by the fire 
underwriters, and if any of them are violated the in- 



ILLUSTRATED 

■ „ T F.VTVRE ON TWO WALL SWITCHES. 

i| , ;:^c^ 1 oN-EL E c TR1 cP ER co, A To R . 

' r v l-'TC ON SIDEBOARD. 

, n^ACHAPLE ELECTR.C TOASTER ON DlNING TABLE W.TH 

3 P Ttlfts CONNECTED TO FLOOR BOX. 

i B A«»OARD OUTLET ON PORCH. 

:,, MBD OUTLET FOR PIANO LAMP. 
5 UASEBUA op Dresser _ 

? SSSSffi^ FOB CE,L,NC LIGHTS AND CHAN- 

, s^rTte' Switches for Pairs of Lights on 
shower fixture. 

9 CONNECTIONS FOR ELECTRIC WASHER 

AND ELECTRIC IRON. CORD 
SUPPORT. 

10 SMALL READ- 



ON SCREENED 
PORCH. 

11 Picture Light- 
■ ing Fixture 
Controlled 
by Switch. 




Courtesy of Electric City Magazine. 



Fig. 279.- 



-Circuits for electric lighted residence. 



Facing page 316 



HOUSE WIRING 317 

surance on the house is canceled. If a fire started for 
any reason in a house with defective wiring the insu- 
rance companies could refuse to pay the loss and would 
probably do so. On this account it pays to do the work 
carefully, and have the job inspected before the wiring 
is concealed or the current turned on. In order to 
learn just what all the rulings on wiring are it is advis- 
able to read carefully a copy of the latest edition of the 
Underwriters' Rules. These can be secured from your 
insurance agent or the Underwriters' Laboratory, 
Chicago. Everybody who is going to do wiring around 
any sort of building should be familiar with these rules. 



CHAPTER XIV 

Private Electric Plants 

Every farm boy has the advantage of fresh country 
air, ample sunlight, and many other things that the 
shut-in city boy misses. He is doubly lucky in this 
electrical age because he can add many of the city ad- 
vantages to his more healthful country home. Almost 
any farm or suburban home can have electric lights 
now. The convenient plants sold all ready to run are 
just as independent and give the same service as the 
big generating stations. The handy little gasoline 
engine does, on a small scale, the same work as the 
immense turbines or big engines of the city plant, and 
provides power to light anywhere from twenty lights 
up to as many as the largest dwelling would need. 

A really complete plant in the basement of your home 
brings the convenience of the city right in your door. 
Light from the dynamo is just as steady and reliable 
as you could secure anywhere. With a set of this sort 
mother can enjoy her electric flat-iron; her hard work of 
washing will be driven away by electricity; and every- 
body can enjoy the toaster, coffee percolator, and 
electric fan. 

3i8 



PRIVATE ELECTRIC PLANTS 319 

The diagram in Fig. 279 indicated how the circuits 
ran in a big city house, and showed some of the uses 
of electricity in it. There are even more in a country 
home. A circuit run to the barn allows light for milk- 
ing, and prevents that chance of fire which always used 
to exist when you took a lantern near a kicking cow. 
A motor in the barn or workshop can turn a line shaft 
to which the feed mill, grindstone, lathe, or other 
machinery can be belted. If there is a forge and 
machine shop the motor will be especially convenient. 
Remember that a motor of this kind is not to be run 



ht TTTTT 



Fig. 280. — Simple plant. 

from the storage batteries. Always start the engine 
up, as the load is apt to be too heavy. The engine 
should also be used whenever a flat-iron is connected, 
or the battery would be ruined in short order. 

Of course, the engine and electric generator are the 
big parts of such a plant, and would supply current for 
lighting without either switchboard or battery if con- 
nected according to the simple arrangement in Fig. 
280. These alone would not be very satisfactory, since 
the lights would go out just as soon as the engine 
stopped. If you came in late at night you would need 
matches and a kerosene lamp just as much as ever, and 



320 BOYS' BOOK OF ELECTRICITY 

if electric light was wanted you would have to go and 
start the engine. Even when the plant was running 
there would be a little flicker due to the slight changes 
of speed of the engine. 

An arrangement that avoids some of these troubles 
is made up of an engine and storage battery wired so 
that the lights are always run from the storage battery, 
and the battery is charged in the daytime from the 
generator. While this gives steady light at any time, 
there is the inconvenience of charging the battery a 



aj fois HTn 



nEQor 



Fig. 281. — Battery plant. 

couple of times a week. Figure 281 shows how such 
a set would be wired. The storage battery would have 
to be^big enough in such a plant to supply current for 
at least three or four nights. 

A third scheme combines battery and engine, and 
this is the best of any. In it the lights may be supplied 
with current direct from the generator, from the battery, 
or, what is better still, from the dynamo and battery 
combined. The battery then is said to be "floating " on 
the line. It is always ready to help out if needed, or 



PRIVATE ELECTRIC PLANTS 321 

to be charged if its charge happens to be low. A glance 
at Fig. 282 will tell you just how the different connec- 
tions are made. 

With the ordinary plant the parts that you ought to 
be familiar with are: First, the engine; second, the gen- 
erator; third, the battery; and fourth, the switchboard. 

The engine of a set that is to supply you with first- 
class light must be very steady running. This holds 
even if you have connections made so that the battery 
floats on the line. An engine would naturally try to 



J G 



5\ 




oa 



Fig. 282. — Plant to give power from battery, engine, or both. 

slow down when a lot of extra work is put on it, and 
speed up when this is taken off. This change is ruin- 
ous to good light; so here is where the governor comes 
in. Its duty is to help the engine along a little when 
it wants to slow down, and to hold it back when it 
tries to speed up. With the governor set just right 
the change in load affects the engine very little. 

As to methods of keeping the speed steady, there 
are two schemes that are quite commonly used: the 
" hit-and-miss" system and the "throttling governor/' 

21 



322 BOYS' BOOK OF ELECTRICITY 

In the first the speed is regulated by missing explosions; 
that is, when the engine is loaded down there is a 
charge taken in and ignited at every stroke. When 




bo 



the speed runs a little higher the engine misses explo- 
sions and naturally slows down. With the throttling 
governor there are no explosions missed at all. When 
the engine is working hard it gets a full supply of 




Fig. 284. — A private electric plant. 



323 



3 2 4 BOYS' BOOK OF ELECTRICITY 

gasoline; as the load is taken off the gasoline supply 
is cut off little by little. This arrangement is so deli- 
cate that even with rapidly changing load the engine 
speed always remains practically the same. 

Generators are built either for the standard no volts 
or for 30 volts. Practically the only advantage of the 
higher voltage is that it permits the use of standard no- 
volt motors, heating appliances, and so on. On the 
other hand, the lower voltage has a very considerable 
advantage. In the first place, it is safer. Further, it 
allows storage batteries to be used to much better ad- 
vantage. For 30 volts, 16 cells in series fill the require- 
ments perfectly. With no volts 55 or more cells would 
be needed; such a number would be very expensive 
and take up far too much room. 

For storage cells either the new nickel-iron or the 
lead cell can be used. The lead costs a little less and 
answers all purposes just as well, since it does not need 
to be moved, and is in a position where it should always 
receive good care. Remember that the life of a storage 
battery depends more on the way it is used than on the 
work it does. 

The switchboard is really the nervous center of your 
plant, especially if it is the automatic or semi-auto- 
matic type. On a semi-automatic board, for instance, 
there would be three switches: one in the lighting cir- 
cuit, one in the battery circuit, and a small single-pole 
switch for ignition. With these the batteries can be 



PRIVATE ELECTRIC PLANTS 



325 



used alone, the engine can be used alone, or engine and 
batteries can be used together, with the batteries acting 
as an electrical "balance wheel." On the back of the 
switchboard is an automatic cut-out which is between 
the battery and dynamo, and opens when the dynamo 
stops or even falls below a certain speed. A voltmeter 
and ammeter on this board tell the operator the elec- 
trical condition of his circuits. 



AN UP-TO-DATE SET 



The plant illustrated in Fig. 285 is one of the most 
desirable for general lighting of farms and country 




Fig. 285. — The engine and dynamo of this set are mounted on the same shaft. 

homes. The vertical engine runs either on kerosene or 
gasoline, using one fuel as efficiently as the other. 
The shaft of the direct-current generator runs in ball- 
bearings, so that a very small part of the power gener- 



326 BOYS' BOOK OF ELECTRICITY 

ated is lost in friction. At the right of the engine is 
shown the storage battery. This supplies light when- 
ever the engine is not running. 

In complete sets of this sort the storage battery helps 
in other ways than just by giving light at odd times. 
In the style known as the "semi-automatic" it cranks 
up the engine in much the same way as the most modern 
electric starters that are installed in automobiles. 
The dynamo is temporarily run as a motor. It turns 
the engine over strongly a few times. As soon as gaso- 
line and air are drawn into the cylinder and ignited 
the engine speeds up and the dynamo is again convert- 
ing work into electricity instead of changing the elec- 
tricity from the storage battery into work. When the 
battery is charged and the engine running the cells act 
as a sort of shock absorber; that is, the little variations 
in generator voltage are smoothed right out and the 
light is made perfectly even and regular. 

When in use every night such a "semi-automatic" 
set needs very little attention indeed. The chances are 
that it will run best when let entirely alone except for 
oiling, cleaning, and charging, according to directions 
which the manufacturers always supply. Of course, 
water will have to be added to the cells once in awhile, 
but never put acid in except when you clean the sedi- 
ment from the bottom of the jars. The water should 
be pure; use distilled water if it can be had. 

Sets without the "semi-automatic" feature are made 



PRIVATE ELECTRIC PLANTS 327 

with an engine entirely separate from the dynamo, the 
power being carried by leather belting. Of course, the 
advantage of such an arrangement is that you can use 
the engine for other work by simply slipping the belt 
off the dynamo and putting it on the pulley of the line 
shaft or whatever you want to drive. Such a plant is 
illustrated in Fig. 283. 

By taking the case of a particular house you can 
form some idea of estimating the needs of a private 
lighting plant. Suppose the house has ten rooms in 
all. There is the library, sitting-room, dining-room, 
kitchen, and one bedroom downstairs. Upstairs are 
four bedrooms and a billiard room. This would re- 
quire about 25 lights, and they could be arranged to 
advantage as follows: 

Library 4 

Living-room 4 

Dining-room 4 

Kitchen 1 

Pantry 1 

Billiard-room 1 

Bedrooms 4 

Bath-room 1 

Hall 3 

Porch 1 

Cellar 1 

Total 25 

For general use 20-watt lamps, which give about 
16 candle-power, are usually considered big enough. 
With a 30-volt plant each of these lamps would take a 



328 BOYS' BOOK OF ELECTRICITY 

current of f ampere. With all the lamps burning there 
would be about 15 amperes flowing in the main con- 
ducting wires. For use on these circuits wire at least 
as large as No. 10 rubber covered would be needed. 
No. 1 2 could be used for the branches. It can be run 
in any of the ways described in the preceding chapter. 
The storage battery has to meet two requirements: 
It must be of the right voltage, which depends on the 
number of the cells alone, and it must have enough cur- 
rent capacity to supply the lamps commonly used for 
at least one entire evening, which depends only on the 
size of the cell. For the plant described the capacity 
should be 50 ampere-hours or more. It would then 
run all the necessary lights if the plant should fail. 
For instance, nine of the lights could be burned for ten 
hours, if desired, before the battery had to be recharged. 
As the best plants are made now, the battery is charged 
whenever the number of lights is small, and helps out 
the engine when extra work is put on it. 

COST OF ELECTRIC LIGHTS 

Of course, the deciding question in putting in electric 
light on a farm or in a country home is very often one 
of expense. "How much will the light cost?" This 
depends very much on circumstances, but you can al- 
ways figure quite closely for your own conditions. 
After you have decided just how many lamps you want, 
estimate how many are apt to be lit at once and how 



PRIVATE ELECTRIC PLANTS 329 

many hours every night each one will burn. This will 
allow you to figure both the kilowatts needed and the 
kilowatt hours used. For instance, if 10 lamps burned 
four hours each, the current consumed would amount 
to 40 lamp-hours, or since each lamp takes about f of 
an ampere it would be f X 40, or 30 ampere-hours. 
The E. M. F. of the system is 30 volts, so the power 
delivered would be 900 watt-hours. For safety a 1- 
kilowatt generator and a ij-horse-power engine would 
probably be used, since as many as 20 lights might be 
lighted at one time. At medium loads the engine would 
probably use slightly more than 1 pint of gasoline an 
hour. For the whole evening, say from 7 until n, 
about I gallon would be used. This would make each 
light for the evening cost about a cent for its four 
hours' use. So electricity, even when you generate it 
yourself, is very cheap when the great convenience of 
it is considered. 



CHAPTER XV 

Gas Engine and Automobile Electricity 

Anybody around a farm or shop will tell you that the 
fellow who can find out what the trouble is, and make 
necessary repairs when anything goes wrong with a 
piece of machinery, is just as big a help as the one who 
is clever at building labor-saving devices. Where a 
gasoline engine is in use you will always be welcome if 
you can point quickly to the source of trouble when 
there is a hitch and set matters right again. It is not 
such a trick after all, if you go about it systematically 
and study the most common causes of trouble. 

First, it is necessary to understand the principle of 
the internal combustion engine. "Internal combus- 
tion" means that the fuel is burned inside the cylinder 
instead of at some outside point under a boiler. At 
the bottom of the whole thing is the fact that a hot 
gas takes up a great deal more room than a cooler one. 
You can prove this to yourself by holding a toy balloon 
near a stove. As the balloon gets warmer it grows 
larger and larger; then the pressure is too great for the 
rubber to hold and the balloon explodes. 

In the gasoline engine the heat is supplied by gasoline 

330 



GAS ENGINE ELECTRICITY 



33* 



vapor and air that comes into the cylinder. An electric 
spark sets fire to the mixture, and it expands with a 
good deal of force. There is no way for it to escape, so 
it pushes the piston outward. In doing this the action 
is just about like that in a small cannon. With the 
cannon the explosive mixture in the form of powder 
is packed behind the projectile. A cap ignites the 
charge; the gas presses with a sudden and enormous 
energy, and the shell starts on its way. In the engine 
the gasoline and air take the place of the powder, and 



Gasoline 
Vapor 




Fig. 286. — How spark ignites gasoline mixture and turns flywheel. 

you have a piston instead of a shell. A strong piston 
rod and crank keep the piston from being blown clear 
out; the flywheel, added to these, helps to turn the 
violent explosions into useful work. The carburetor 
simply mixes the gas and air in the right proportions; 
the valves allow the mixture to be taken in and the 
burned gases disposed of. 

In this general way practically all gasoline engines 
are alike. The first big difference to consider is in the 
way the gas comes into the cylinder and the way it is 



332 BOYS' BOOK OF ELECTRICITY 

got rid of. This divides the engines into " two-cycle' ' 
and " four-cycle " machines. The word "cycle" means a 
complete round of motions. To go back to the cannon : 
a " cannon-cycle" would be, first, loading; second, 
firing; third, taking out the empty shell. Then you 
would start all over. In the engine, ' ' two-cycle ' ' means 
that there are two strokes to a cycle; "four-cycle," 
that there are four strokes to each complete set of 
movements. The proper names for the cycles of these 
engines would really be "two-stroke cycle" and "four- 
stroke cycle," but these terms are too long for common 
use. 

You will see the difference more clearly by following 
out the movement in each case. In the two-cycle 
engine these are: 

Expansion Stroke. — Electric spark ignites explosive 
mixture of air and gasoline in cylinder, forcing the 
piston outward. At the end of this stroke a "port" 
is uncovered, allowing gas to rush in from the crank case 
and force the burned gases out. 

Compression Stroke. — Gas is compressed ready for 
another ignition, and at the same time a new charge is 
drawn into the crank case. 

In the four-cycle type of engine the spark comes only 
half as often. The cycle here is as follows: 

Intake Stroke. — Explosive mixture of fuel and gaso- 
line is drawn into the cylinder. 

Compression Stroke. — Valves are closed and explo- 



GAS ENGINE ELECTRICITY 333 

sive mixture is compressed. Just before this stroke is 
finished the spark occurs and the mixture is ignited. 

Power Stroke. — The piston is driven outward and 
the flywheel turned. 

Exhaust Stroke. — Piston carried back again expels the 
burned gases from the cylinder. This completes the 
four operations of the cycle. 

Each of these engines has its special field. The two- 
cycle type, which runs at slower speed, is very widely 
used for motor-boats, and also to supply power for 
shop and farm work. Four-cycle engines are made in 
all sizes and used for all purposes. Many gasoline 
and kerosene engines are made in this type. Auto- 
mobile engines and racing-boat engines are all four- 
cycle engines. 

In both cases the ignition or explosion of gas is 
brought about by an electric spark. It may be pro- 
duced either by a spark-plug or by a make-and-break 
arrangement, but the important things are that it must 
always be hot enough to ignite the explosive mixture, 
and that it is timed to jump at just the right instant. 

The spark-plug is simply a spark-gap like the one 
described in Chapter V. A set of batteries is con- 
nected in the primary of an induction-coil and a con- 
tact arranged so that the circuit is closed and broken 
at just the proper instant. The low voltage current in 
the primary then induces a much higher one in the 
secondary, and a hot little spark jumps across the space 



334 



BOYS' BOOK OF ELECTRICITY 



between the metal terminals of the plug. The gasoline 
mixture around it ignites and the piston is pushed out- 
ward. This is the process of high-tension ignition. 

With a make-and-break system a much more reliable 
spark is claimed, and only a very simple and small 
coil is needed. With this, one of the points inside the 




Fig. 287. — Make-and-break igniter. 



Fig. 288 — 
Spark-plug. 



cylinder is fixed solid; the other one moves. At the 
right time they touch together, and then are suddenly 
pulled apart at the proper moment by a little latch and 
trip arrangement geared to the shaft. A spark passes 
when the break is made and the explosive gas is ignited. 
On account of the low voltage used the make-and-break 
scheme is sometimes called low-tension ignition. It is 
wired as shown in Fig. 290, when used with a magneto, 



GAS ENGINE ELECTRICITY 335 




Fig. 289.— Electrical parts of make-and-break ignition system: A, Mag- 
neto; B, magneto gear; C, igniter trip rod; D, igniter; £, connection from 
magneto to igniter. 



WIRE CONNECTED 
TO ENGINE FRAME 




iii'lninriiiiian^TTT 



a 



CLOSE SWITCH 
TO STOP INSULATED TERMINAL 



OF IGNITER 

Fig. 290. — Connection for magneto with make-and-break ignition. 



or as in Fig. 291, where combination battery and 
magneto arrangement is desired. 

Some experts claim that the jump spark is best, and 



33^ 



BOYS' BOOK OF ELECTRICITY 



others stand up for the make and break; each one of 
them has good points that are not disputed. For 
automobiles and high-speed marine engines the jump 
spark is always used. For lower speed stationary 
machines the reliability of the make and break is a 
strong point in its favor. 

When you hunt for spark trouble in either one of the 
systems have a regular method and stick to it, no matter 
what you think the fault might be. 




Loorreo line shows path of current 

I THROUGH EMSI " 



Fig. 291. — Wiring for both battery and magneto. 



This may take a little longer in some cases, but it 
generally saves time in the end. Weak spots are less 
liable to be overlooked. Here is one method that you 
can follow: First, see that the igniter switch is closed. 
If the engine has a jump spark, the next thing is to un- 
screw the terminal from the plug and hold the end very 
close to the end connection. Have some one give the 
flywheel a few quick turns. If the spark jumps across 
the little gap, you may be sure that the ignition is all 



GAS ENGINE ELECTRICITY 337 

right. If not, any one of several things may be the 
matter. 

First, trace the wiring right from the batteries, and 
make sure that all connections are tight and that no 
wires are broken. Sometimes a break is quite hard to 
find on account of the heavy insulation. Look over 
the insulation and see that it is not worn or scraped off 
at any point. Next unscrew the spark-plug and see 
that the little points are perfectly clean. The carbon 
deposit that sometimes forms on them hinders or even 
prevents passage of the spark. This deposit must be 
cleaned off with a fine file or a piece of sandpaper. 
Make sure, too, that the wire tips are separated by just 
the right distance. There should be just room enough 
to slip a worn dime between the two points. 

If the engine uses a make-and-break system, the elec- 
trodes should be taken out and examined to see if they 
touch together, also to find if they separate properly 
when the latch is tripped. Sometimes the little buttons 
become worn; if this is the case, they can be removed 
and new ones put in with very little trouble. 

Of course, there may be other causes of a tie-up, such 
as a bad mixture of gas or carburetor trouble, but these 
can be traced out and each gone after in its own way. 
By keeping the engine clean, using new batteries* and 
watching for insulation trouble you will be able to very 
largely avoid all ignition trouble, whether you use dry 
batteries or magneto, jump spark or make and break. 



338 



BOYS' BOOK OF ELECTRICITY 



AUTOMOBILE ELECTRICITY 

In an automobile the ignition is a little more com- 
plicated. There are four or more sparks instead of one. 
They must all be strong and must come at just the right 
time. In addition to the wiring for ignition there is the 
lighting system, the storage battery, and the self-starter. 



Ignition Terminals 




Distributor Plate 



C=D 






Interrupter Cover 



-Oil 



>e 



nterruptefContects 



D 



Fig. 292. — Automobile ignition unit. 

All of this makes rather a complex arrangement of elec- 
trical apparatus on the automobile. Some cars have 
six circuits or even more, with a separate fuse for each 
circuit, and wiring almost as complicated as in a factory 
using motors and lamps. The up-to-date machines 
use a motor for starting, a generator for lighting and 



AUTOMOBILE ELECTRICITY 



339 



ignition, and a storage battery to serve the two. Even 
the common forms of ignition device are far from being 
simple. One of these is illustrated in Fig. 292. From 
the diagram of this (Fig. 293) it will be seen that the 
main parts are: (1) Induction-coil; (2) Condenser; 



:£ To Sparh Plugs'. 



Distributer Brushes 
[K^^z^A/no-uction Coil 



Condenser 




dotten 



Fig. 293. — Ignition system for automobile. 

(3) Interrupter; (4) Distributor — each with a very 
definite duty. The coil raises the voltage to the point 
where a spark jumps between the spark-plug points. 
The interruptor breaks the primary circuit. The con- 
denser makes the break very sudden. The distributor 



34Q 



BOYS' BOOK OF ELECTRICITY 



simply directs the spark to each cylinder in its proper 
turn. 

For lighting alone an electric generator driven from 
the engine shaft either by a belt, chain, or gears is 
used. This supplies direct current, and is used with a 
set of storage cells, so that the lamps can be lighted 
whether the engine is running or not. In connection 
with such a system a regulator has to be used. Other- 
wisethe lamps would burn out if the engine ran very- 
fast, or they would be very dim when the engine ran 




^P T Extra 



] ! Generator 



' "| Li qh ting 



Li anting 
Switch 







Grounded Return 'Circuit' 

Fig. 294. — How automobile lights are wired. 

slowly. When the engine is not running at all the lights 
are supplied by the battery. The principle of such a 
regulator is indicated in Fig. 294. As the engine comes 
to a speed that corresponds with about eight miles an 
hour the switch closes and the generator supplies cur- 
rent. When the engine goes still faster the little 
switch opens and closes very rapidly, so that the voltage 
at the lamps is cut down by just the proper amount. 
A complete diagram of wiring for automobile lamps is 
shown in Fig. 295. 



AUTOMOBILE ELECTRICITY 



34i 



Ignition and lighting systems are often combined, so 
that current is supplied for both purposes by one 



HSAD imp 

HEAD LASP 



*m 



m 




Fig. 295. — How an automobile is wired. 

generator, helped out by a set of storage cells. This 
arrangement is shown in Fig. 296. 



High Tension^ 



Low Tension 




\Lights 



Grounded Return Circuit 
Fig. 296. — Lighting and ignition system. 

With a little extra machinery and wiring a generator 
and motor can do all the work of ignition, lighting, 
and also start the engine. Such systems are saving a 



342 BOYS' BOOK OF ELECTRICITY 

lot of work for motorists, but sometimes cause more or 
less annoyance. Nothing is more annoying than an 
electric starter that does not start. The inside of one 
of these electric starters is so simple that a little search 
will generally show what trouble exists, if you under- 
stand just what the action is. In the first place, the 
power is supplied by a motor connected to a set of 
storage batteries and geared to the engine shaft. The 
motor runs much faster than the engine. On one system 
the little gear is slid into position with a foot lever. The 
same motion closes a switch and starts the motor at 
worli. When the engine takes hold and reaches a cer- 
tain speed it throws the pinion and gear out of mesh, 
open^ the switch, and stops the motor. You can trace 
the .connection on a system of this sort from Fig. 
297. 

Another starting system does away with the foot 
lever entirely. With this you simply press a button. 
A switch closes and the motor starts. The pinion is 
not keyed fast onto the shaft, but runs loosely on a 
thread. It is forced into position by the thread when- 
ever the motor is started. One thing necessary is that 
the teeth must always strike together properly and 
must never lock. This is provided for by making the 
shaft of the pinion in two pieces. They are held to- 
gether by a strong spiral spring. There is always a 
little give to the spring, so that the pinion slips until it 
comes into the proper position and the teeth of the 



AUTOMOBILE ELECTRICITY 



343 




Fig. 297. — Electric starter operated with foot pedal. 



pinion slide into mesh with those of the gear. You 
can see how this arrangement works by referring to 



344 



BOYS' BOOK OF ELECTRICITY 



Fig. 298. As nearly all the systems use batteries, a 
word about their care will not be out of place. To 
begin with, see that the cells are kept charged and 
that the liquid is kept at the same level all the time. 
Remember that only the water evaporates, so only pure 
water should be added. 

The batteries which are used carefully, kept filled 
with distilled water to a proper level, and let alone are 



Storting Motor 



{/ectro -Magnetic M > 
Storting Snitch 



.Starting Motor 




Fig. 298. — Electric starter with hand or foot switch and push-button. 



the ones that give best service. It is not use but 
abuse that wears out storage batteries. 

Wiring is much the same in all the systems. The 
current is usually carried one way on heavily insulated 
cable, and returns through the iron frame of the engine 
and automobile. This simplifies the work of hunting 
for trouble a good deal, as you only have to look over 
about half the length of wire you would otherwise need 
to inspect. As to the actual method of running the 



AUTOMOBILE ELECTRICITY 345 

wiring, it is best to familiarize yourself with whatever 
system is used on the car you are interested in. Follow 
out the wiring and find just where each wire goes, and 
why. Learn what each switch controls. Then when 
there is any trouble with the electrical equipment you 
will be prepared to trace it down. 



CHAPTER XVI 

Making and Installing Lamps and Fixtures 

If you have furnished your room with the Mission 
chairs, table, and other pieces described in the Ameri- 
can Boys' Workshop you can go right ahead and make 
lamps that fit in with the rest, and will add a good deal 
to the appearance and effect of all the furniture. They 
are really not so hard to make as some of the other 
pieces of electrical equipment, and are extremely useful 
in a plain everyday way. 

At first thought it may seem that colored glass, 
brass work, and so on, are needed to make even the 
simplest sort of lamp, but these are not really necessary, 
at least to begin with. Of course, substantial woodwork 
is necessary for the base, or support, but very good 
shades can be made from even such simple materials 
as cardboard and colored tissue-paper. Do not try 
to use heavy pasteboard for the work, but secure a sheet 
of the thinner, tougher Bristol board. This will fold 
along a crease without weakening or cracking. 

As a first trial in lamp-shade making a simple shade 
should be fixed for a drop light. If the work is neat 
the result will be surprisingly attractive, and will give 
you the experience to go ahead successfully with bigger 

34 6 



MAKING LAMPS AND FIXTURES 347 

shades. For this a piece of Bristol board 10 by 20 
inches will be the principal need. Mark this out care- 




fully with a sharp lead pencil in the form illustrated by 
Fig. 299. This must be done accurately or the shade 



348 BOYS' BOOK OF ELECTRICITY 

will never look right. Cut out along the lines marked 
with the heavy line, and then along each one of the 
dotted lines mark with a table knife or the back of a 
penknife blade. This should be done with a ruler so 
that the mark will be perfectly straight. It then makes 
folding easy and insures a straight, neat fold. The pat- 
terns on the shade should be cut with a 'very sharp 




Fig. 300. — Finished shade for drop light. 

knife. This makes a much better job than is possible 
with shears. 

The shade is now ready to be folded and pasted. 
The little end flap "A" should be pasted under the 
corner, and the top flaps are simply pasted firmly one 
on top of the other. After the paste has dried mark 
out a circle on the top, using a lamp socket for drawing 



MAKING LAMPS AND FIXTURES 349 

the mark to the proper size. Cut just inside the line 
with a sharp knife, and slip over the ring at the end of 
the lamp socket. The shade will thus be held firmly in 
place and will be properly placed on the socket. 

Larger shades can be made in much the same way for 
lamps already in use. It cannot be expected that these 
will last quite as long or stand the hard knocks as well 
as a shade made from sheet brass, but there are many 





Lamp 
Cord 

Fig. 301. — Mounting the socket on the standard. 

places where they answer quite as well. They are so 
cheap and easily made that the whole house can be 
decorated with them for a Hallowe'en party or St. 
Patrick's Day party without much time or money being 
put into the work. 

If you want to make an entire table lamp that is 
both substantial and decorative you will need to do a 
little carpenter work, some glass cutting, and metal 



35o 



BOYS' BOOK OF ELECTRICITY 



working. The result will more than pay you, for the 
lamp will be really substantial and the equal of one you 
would buy. As to materials, the principal things 
needed are a piece of |-inch board for the standard, a 





Fig. 302. — Table lamp. 

i -inch board for the base, and a sheet of brass or copper 
17 by 17 inches in size. 

Make the base 7 inches square and mortise a square 
hole in the center as shown. The standard is made of 
the J-inch strips fastened with small brads. In the 
top of this the lamp socket is fastened firmly by screw- 



MAKING LAMPS AND FIXTURES 351 

ing it on a piece of f - or J-inch pipe fixed in a block of 
wood, and the lamp cord dropped down through the hol- 
low standard. By cutting a groove outward along the 
bottom of the base, and boring a hole upward, the cord 
is brought out for connection to the socket. Four 
supports for the shade complete the standard of the 
lamp. These should be made from sheet-brass strips 
each 6| inches long. Two holes bored through one end 




Fig. 303. — How cord runs to lamp. 

receive the screws that hold the brass to the standard, 
while the other tip is turned up slightly to hold the shade 
in place. 

For the shade, cut the sheet-brass with tin shears ac- 
cording to Fig. 304. The bends should be made over 
the edge of a vise so that they will be true and work- 
manlike. Bore f-inch holes to fasten the edges to- 
gether and the top piece in place. Considerable care 



35 2 



BOYS' BOOK OF ELECTRICITY 



should be taken with the riveting, as any faults in this 
respect are apt to show up quite plainly. 

At this point the four pieces of colored glass should be 
cut to fit. They are held in place by the four little 
tongues that were left when the sheet of brass was cut. 




Fig. 304. — Shade for table lamp. 



These should be bent over the glass just as firmly as 
possible so that there is no chance of the pieces rattling. 
The base can now be stained with the desired color 
and the brass work finished. If it is desired to have 
this remain bright a coat or two of lacquer should be 
applied. This keeps the metal from tarnishing. 



MAKING LAMPS AND FIXTURES 353 

If you want pretty lights on the wall they can be made 
in much the same way. These are really more for 
decoration than for light, and so smaller lamps than 
usual can be used with good results. The bracket 
which supports the lamp is made hollow, and built in 




Fig. 305. — Dimensions of table lamp. 



about the same manner as the table lamp already de- 
scribed. 

For general illumination the shower fixture is used a 
great deal, is quite decorative, and no harder to make 
than an ordinary two- or f our-light chandelier. For the 
23 



354 BOYS' BOOK OF ELECTRICITY 

fixture shown (Fig. 306) the four shades may be made 
from either light wood or fibre board. These can be 
cut in a design similar to the one shown in Fig. 308, 
and colored glass or tissue-paper put inside to give 
the art-glass lamp effect. In the top piece of the shade 
a hole may be made for the brass tip of the socket. In 
this socket screw a J-inch piece of f-inch iron pipe. 




Fig. 306. — Shower fixture. 

The shade and lamp will then be held up by this pipe. 
A hole bored through the end of the pipe will take one 
link of the chain as indicated in Fig. 307. The other 
end of the chain is to be linked with a screw-eye fastened 
to the ceiling plate. Four pieces of chain cut to the 
same length will be needed. The ceiling plate can be 
very simply made from two pieces of i-inch board 
joined in the middle at right angles. The conductors 



MAKING LAMPS AND FIXTURES 355 



Threaded Iron Pip* 




f \ 

Fig- 307. — How shade is fastened to chain. 




Fig. 308. — Side for shower fixture shade. 

can be run in grooves in the upper side of the arms, and 
are usually carried down to the lights intertwined with 
the links of the chain. 
A little desk light such as the one illustrated in Fig. 



356 



BOYS' BOOK OF ELECTRICITY 



309 makes a very attractive gift and is even easier to 
make up than the large table lamp. For this the shade 
may be cut out of thin wood with a scroll saw or made 
of heavy cardboard. The stand can be made either of 
a hollow piece or solid with a hole bored through it 




Fig. 309. — Desk lamp. 

for the cord. The socket used should be provided with 
a pull-chain. 

For the living-room a piano lamp is both convenient 
and ornamental. This can be made according to Fig. 
312, from a piece of 2 -inch square material for the 



MAKING LAMPS AND FIXTURES 357 

center, and four strips of f-inch board for legs. The 
legs should be very carefully marked, and should all 
curve just exactly alike. The best way of getting the 
same shape is to cut a pattern from stiff paper, fasten 
it to the wood with pins or small tacks, and mark care- 




Fig. 310. — Details of desk lamp. 

fully around the edge. The legs can be attached with 
long screws or pegs to the square central post. To con- 
ceal the wires one of them may be run in a groove under 
each of two legs. Of coli&e, a long hole will have to 
be bored down the centerpiece to start the wires 
through. In this hole put apiece of J- or J-inch iron 



358 



BOYS' BOOK OF ELECTRICITY 



pipe. To this fix a "tee," and in the "tee" screw 
two pieces of short threaded pipe bent to a small angle. 
Sockets with the proper sized threaded part may be 
screwed right on these pipes, and the joint will be very 
solid. This practically completes the lamp standard. 
Additional pieces may be set at the bottom for greater 




Fixture Plate 



Ceilings "-A^- 



1 





Fig. 31 x. — How fixture is hung by fastening to fixture plate. 

strength if desired. Staining depends on the finish 
of the other furniture. 

A very attractive silk shade can be made on a simple 
wire frame by mother or sjs£er. This frame should be 
supported by four wire£ ( running upward from a point 
near the top of the standard. 



MAKING LAMPS AND FIXTURES 359 



All of these shades are decorative as well as useful, 
and considerable attention should be paid to the work- 





Fig. 312. — Dimensions of piano Fig. 313. — Finished piano lamp, 
lamp. 

manship in them. The boards should be plained very 
smoothly, and then rubbed down with fine sandpaper. 



360 BOYS' BOOK OF ELECTRICITY 

After this they can either be polished or stained to 
match the other furnishings of the room. 

The glass may be any color that is obtainable. Green 
is probably the best, as it is generally considered restful 
to the eyes. Do not make the mistake of using a lot of 
pieces of different colors. The result will be much 
better if you stick to the same style and tints in all the 
lamps that you build. 

When it comes to installing these lamps, the most 
important thing is to see that they are fixed firmly in 
place. For the chandelier long screws should be used, 
and these should run through the plaster and lath of 
the ceiling and into a wooden plate set between the 
rafters as described in Chapter XIII. There is no 
chance then of its falling down the first time it is sub- 
jected to a heavy or unusual strain. Placing the lamps 
in the rooms or around the walls is largely a matter of 
taste. The matter of wiring has to be considered as 
well as the effect you want to produce. Well-placed 
lamps, solidly built and firmly set in place, are indeed a 
credit to any boy. If he has wired his home, as well 
as built and installed the fixtures, he may well consider 
that his knowledge of the principles of electricity has 
brought him a large and permanent return. Through 
the work of his own hands he has enabled himself and 
his family to enjoy the greatest and best of our elec- 
trical blessings — electric light. 



INDEX 



Acid for storage cells, 83; care in 

handling, 77; mixing with water, 78 
Aerial conductor, 263; construction, 

261; spreader, 264; strain insulator, 

264 
Aerials, kinds of, 262; purpose of, 253 
Agonic line, 14 
Alarm, burglar, no 
Alternating current, 177 
Amalgam for primary cells, 65; for 

static machine, 45 
Amber 28 
Ampere, 90 

Annunciator, three-call, 113 
Anode, 132 
Arc, 147 
Arc lamp, 151 

Armature for bell, 104; motor, 205 
Automobile electricity, 338; lighting, 

340; starters, 342; wiring, 344 

B 

Battery, definition of, 63; discovery 

of, 61; nature of, 61 
Bells, circuit for, 101; how to make, 

102; principle of, 101; wiring for, 

108 
Bell's telephone, 230 
Binding-posts, 106 
Bluestone, 67 



Burglar alarm, no; how to wire, in 
Buzzer test, 293 



Candlepower, 151 

Carborundum, 147 

Cathode, 132 

Catlin grip, 223 

Ceiling lamp fixture, 358 

Cell, action visible in, 64; carbon cyl- 
inder, 66; choosing the right, 84; 
Daniell, 66; definition of 62; dry, 
68; gravity, 68; Leclanche, 66; 
making a dry, 73; making a pri- 
mary, 69; single fluid, 74; storage, 
79; tomato can, 72 

Cells, electrodes for, 75; forms of, 65, 
66, 67, 68; voltage of, 78 

Central station, first, 158 

Chemicals, handling, 77 

Circuit, definition of, 86 

Circuits for house wiring, 316 

Clock light, 164 

Close coupling for wireless sets, 259 

Coherer, 296 

Coil, sections for induction, 122 

Coil winding for bells, 103 

Collector rings, 177 

Color, 149, 150 

"Columbia," voyage of the, 158 

Commutator, 173, 198, 206 
361 



362 



INDEX 



Compass, 12; early forms of, 13; 
modern, 14; stories of, 12 

Compound winding, 176 

Condenser, 127; fixed, for wireless, 
278; glass plate, 289; test-tube, 
290; variable, for wireless, 279 

Conductors, 32 

Conduit, 315 

Connections for annunciator, 115; 
for battery, 78; for buzzer test, 293 ; 
for coherer, relay and sounder, 297; 
for induction coil, 117; for induc- 
tion coil and spark gap, 127; for 
lamp and wall switch, 310; for 
microphone, 244; parallel, 49, 79, 
93; series, 49, 79, 935 telegraph, 
219, 222; telephone, 230; telephone 
with induction coil, 249; wireless 
sets, 258, 259, 260 

Core of induction coil, 1 19 

Core, transformer, 179 

Cost of electric light, 328 

"Crow's foot," 68 

Current and voltage compared to 
flow of water, 86 

Current, alternating, 177; direct, 173; 
direction of, in cell, 63; electric, 61 

Cycle, 177 

D 

Darkroom lamp, 166 

Davy's Samp, 152 

Depolarizer, 65 

Desk lamp, 355 

Desk telephone, 243 

Detectors, use of, 255; cat whisker, 
269; silicon, 270 

Diamagnetic materials, 25 

Diaphragm, telephone, 237 

Dice, the jumping, 53 

Direct current, 173 

Discharger for Leyden jar, 42 

Drop lights, 309 



Dufay, discovery of, 30 

Dynamo, making a, 180; winding of, 

174 

E 
E. M. F., 64; of cells, 78; definition 

of, 91 
Edison's experiments, 157; lamps, 

156 
Electric battery, 61; current, 61 
Electric machine, cylinder, 42 
Electric plants, private, 318 
Electricity, positive and negative, 31; 

static, 27 
Electrodes for single fluid cells, 75, 76 
Electromagnets, 95, 98; uses of, 100 
Electrophorus, 35 
Electropoian fluid, 74 
Electroscope, gold leaf, 40; pith-ball, 

39; paper, 30 
Elektron, 28 

Engines, for electric plants, 321; four- 
cycle, 332; gas, 330; rinding trouble 

in, 336; two-cycle, 332 
Ether, 251 

Exercises in telegraphy, 225 
Experiments with static, 46, 50; with 

spark coil, 129 



Faraday's generator, 169 
Filaments for incandescent lamps, 

157, 158 
Flat-iron, 138 
Fleming's rule, 171 
Flexduct, 308 
Fluoroscope, 132 
Franklin, Benjamin, 55; experiment 

with kite, 33, 34 



Galvani's experiment, 61 
Galvanic battery, 62 



INDEX 



363 



Geissler tubes, 130 

Generators, alternating current, 172; 
development of, 169; direct cur- 
rent, 173; Faraday's first, 169; 
principle of, 168; winding of fields, 

174 
Gilbert, 16, 29, 30 
Gray's experiments, 32 
Grids, 80 
Ground for aerial, 267 

H 

Head set for wireless, 282 

Heating appliances, 136 

Heating, electric, 134 

Helix, 258; making a, 285; clips for, 
288 

Henry's experiments with the tele- 
graph, 208 

Hertzian waves, 252 

House wiring, 299 

I 

Incandescent lamp, 156 

Induction, 116 

Induction coil, 117; making an, 118; 

for telephone, 248; for wireless, 

283 
Insulators, 32, 91 



Keeper for magnet, 26 

Key, telegraph, 213; transmitting, 

for wireless, 284 
Kilowatt, 93 
Kilowatt-hour, 93 
Knob and tube wiring, 304 



Lamp bases, 162 
Lamp shade, paper, 346 



Lamp shade for table lamp, 352 

Lamp, silk shade, 359 

Lamps, sizes of miniature, 167 

Lantern with miniature lamp, 163 

Lead in for aerial, 266 

Leyden jar, 37; invention of, 38 

Lichtenberg figures, 53 

Light, clock, 164; darkroom, 166; 

dividing the electric, 156; facts 

about, 149 
Lightning, 54 
Lightning rod, 56 
Lightning-rod experiments, 59 
Lines of force, 97 
Local action, 65 
Lodestone, 12 
Loose coupler, 275 

M 

Magnet, discovery of, n; experi- 
ments with, 15; horseshoe, 15; 
keeping a, 26; making a, 25 

Magnetic attraction, 17; dip, 14; 
field, 19; lines of force, 20; ma- 
terials, 23; screen effect, 18; spec- 
trum, 23 

Magnetism by induction, 20; theory 
of, 23 

Make and break igniter, 333 

Mazda lamps, 160 

Mercury- vapor lamp, 155 

Microphone, 244 

Miniature lamps, 162; sizes of, 167 

Molecules in iron and steel, 24 

Morse, Samuel B., 209 

Morse alphabet, 224 

Motor, cork, 199; making a, 203; 
principle of, 194; static electric, 51 

N 
Neckham, Alexander, 12 
Negative electricity, 31 



3^4 



INDEX 



Night light, 165 
Non-conductors, 32 
Norman, Robert, 15 
Norman's experiment, 16 



Oersted's discoveries, 97 
Ohm, 91 
Ohm's law, 92 

Oscillation transformer, 261: 
to make an, 288 



how 



Paconnoti's discovery, 196 

Parallel connections for lighting, 93 

Paramagnetic materials, 25 

Piano lamp, 359 

Platinum, 161 

Pockets for wiring, 305 

Polarization, 65 

Poles, north and south, 13 

Positive electricity, 31 

Potential, 64 

Primary of coil, 117; of transformer, 

179 
Push button, 109 



Rat-tail for aerial, 265 

Receiver of telephone, 232; how to 

make, 234 
Reis' telephone, 229 
Relay for burglar alarm, in; for 

telegraph, 213, 220, 221 
Residual magnetism, 174 
Resistance, 90 



Secondary of coil, 1 1 7 ; of transformer, 

179 
Semi-automatic lighting plants, 326 



Sending telegrams, 223 

Series connection for lighting, 93 

Series winding, 174 

Service switch, 303; wires, 314 

Shipwreck, 59 

Shower fixture, 353 

Shunt winding, 174 

Slider, easily made, 274 

Soldering, 308 

Solenoid, 98 

Sound vibrations, 229 

Sounder, telegraph, 211 

Spark design, static, 52 

Spark gap, 127; for wireless, 291 

Spark pane, 51 

Spark plug, 333 

Splices, wire, 109 

Spreader for aerial, 263 

Static electricity, 27; experiments 

with, 46 
Storage cell, making a, 81 
Switch, three-way, 312; two-way, for 

telegraph, 220 
Switchboards, 324 



Table lamp, 350 

Telegraph circuit, 213 

Telegraph, first successful, 209; in- 
struments, 210 

Telegraph set, simple, 214 

Telephone, 228; building a, 234 

Three-way switch, 312 

Thunder house, 59 

Toaster, making a, 142 

Transformer, how to build a, 186; 
step up and step down, 180; wire- 
less, 291 

Transmission of power, 86 

Transmitter, telephone, 232, 238 

Tuner, double-slide, 271 



INDEX 



365 



Tungsten, 160 

Tuning wireless sets, 256 



Van Musschenbroeck, Peter, 38 

Volt, 91 

Volta, 62 

Voltage, 64 

Voltage and current compared to 

flow of water, 86 
Voltage of cells, 78; for small electric 

plants, 324 
Voltaic pile, 62 



W 

Watt, 92 

Wave length, 267; wireless, 257 

Welding, 146 

Winding induction coil, 120 

Wire table, 128 

Wireless laws, 256 

Wireless waves, 252 

Wiring for telegraph circuit, 213 

Wiring in molding, 301 



X-rays, 132 




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